Background: Living evidence (LE) refers to the methodological processes that permit new research findings to be continually incorporated into evidence synthesis. This approach is of great value in the resolution of relevant and rapidly changing clinical questions. To date, the methods to carry out this type of synthesis are not completely defined, and great variability is observed in the approaches used by different groups of authors.Objective: To identify, evaluate and summarise the current methods used for living evidence synthesisMethods: We will conduct a methodological study based on a systematic literature search to identify any type of evidence synthesis such as systematic reviews, network metanalyses and overviews that used “living evidence synthesis” as part of their methods. The search will be conducted in Medline (via PubMed) and Epistemonikos databases. Additionally, we will search websites of the organisations publishing any living evidence synthesis retrieved in the two databases, in order to identify unpublished subsequent reports. Two reviewers will independently assess each article against the selection criteria, extract data on methods and procedures, and assess the methodological quality of each publication. Data will be analysed descriptively. The basis for the “Living Evidence” has been established, however, the way it is carried out and the methods used by investigators are still unknown.This study aims to identify, evaluate and summarise the methods and procedures used by authors to keep the evidence “living”.In order to meet our objective, we will search for all articles reporting a living evidence synthesis to answer a health question. We will search for them in different databases and select the reviews that meet “Living Evidence” characteristics established in advance. We will extract the information related to the methods used by authors to constantly identify new evidence, the procedures used to incorporate the new findings in previous evidence synthesis, and the process followed to inform users of updates. This information will be analysed and presented in a descriptively.. However, SRs often do not have the expected impact; among various reasons that could be mentioned, the rapid outdating of their conclusions is the one that most limits its use and potential impact, making the enormous efforts of developing them largely sterile.The exponential proliferation of scientific studies and their dispersion through a multitude of scientific journals, some of them of limited access for readers, poses a significant challenge to health care professionals, given their limited time to keep permanently updated in their respective disciplines. Therefore, systematic reviews (SR) and other derived evidence synthesis products  are valuable informational tools that try to bring scientific evidence closer to the end-user, facilitating its interpretation and applicationThere are areas of high scientific productivity and controversy in which using outdated information poses a major challenge to clinical practice, and solutions are urgently needed. The methodological approach known as “living evidence” (LE) has emerged as a tool with the potential to address this need. It has been applied mainly to SRs, but currently, it is not uncommon to find other types of evidence synthesis such as overviews and network meta-analysis presented as "living".. When the LE approach is applied to the resolution of relevant and rapidly changing clinical questions, it ensures a rapid update of evidence synthesis that informs on the effects of controversial health interventions, and/or where there are uncertainties.A “living systematic review” is a continually updated SR, which incorporates new relevant evidence as it becomes available. In practice, this means continual surveillance for new research evidence through on going or frequent searches, and the inclusion of new information into the review in a timely manner so that the findings and conclusions of the SR remain currentThe potential for LE to reduce the time and cost of updating evidence-based products such as clinical practice guidelines, health technology evaluations and evidence summaries aimed to inform health decisions (e.g. policy briefs) and making it available to inform practice is enormous; nevertheless, it is necessary to weigh the potential benefits with the overload of time and resources that living synthesis entails. and have been under development over the past few years. These have been used as the basis for the development and application of new strategies to keep the evidence supporting different products up-to-date. It has been of particular interest to synthesise and disseminate the exponential research output published during the COVID-19 pandemic. Being a highly attractive methodology to be applied for many questions in health, but equally recent, little is known about the methods followed by the authors, their validity and the efficiency to achieve an adequate integration of emerging studies in the existing evidence synthesis. Despite some advances in this regard, the methods and quality of living systematic reviews and other types of living evidence synthesis have not been empirically evaluated. There is also no clear route regarding the dissemination process, publication or editorial processes that the periodic updates of the living evidence synthesis follow to reach readers and potential users.The foundations of the LE model for SRs were initially stated in 2014, in order to identify the relevant methodological items that a living evidence synthesis should include.With this study, we seek to identify, evaluate, and summarise the methods and procedures that different groups are currently using to generate and keep the evidence synthesis “living”, and identify those aspects associated with the reliability and maintenance of the methodological quality of that synthesis through its multiple updates. We also aim to identify the different actions carrying out by living evidence synthesis authors to alert users of the evidence changes or periodic updates of the evidence synthesis, particularly when they have implications on clinical decisions and health policies. In this regard, we will explore editorial processes for new publications, informal update alerts, use of web-based repositories, among other actions presented by authors. Finally, we aim to provide suggestions for improving the development and report of living evidence synthesis based on a previous work done by our research team, in which we have reviewed all the methodological and guidance papers published up to July 2021 describing the “living evidence methodology”This study is being conducted as part of a larger knowledge transfer project entitled “Living Evidence to Inform Health Decisions”, funded by the European Union’s Horizon 2020 research and innovation Marie Skłodowska-Curie Action (grant agreement No. 894990). Results of this assessment will contribute to the development of a living evidence implementation framework for health system organizations to use and incorporate LE methodology in the development of knowledge transfer products.This is a cross sectional methodological study in which we will collect data from all living evidence synthesis published reports (articles) identified in the current available literature.Our population of interest is any type of evidence synthesis including systematic reviews, meta-analysis, rapid review, network metanalysis, and overviews that have reported to use "living evidence" (LE) methodology (i.e. living evidence synthesis reports) to answer any clinical questions regardless the LE methodology used.Because our aim is to review the methods used by authors to produce and maintain living evidence synthesis, we will include all “living evidence synthesis” identified, regardless of the type of condition, the participants or populations, the interventions or the exposures, and the alternatives against which the interventions/exposures are being compared.Any of the review types corresponding to the terms “systematic review”; “meta-analysis”; “rapid review”; “review”; “network”; “network meta-analysis”, “scoping review”, “overview” and “evidence synthesis” will be selected if it includes any of the following words or descriptions regarding the use of a living strategy: “continuous updating”, “continuously updated”, “constantly updated”, “continual updating”, “continually updated”, “regular updating”, “regularly updated”, “updated regularly”, “regular updates”, “frequent updating”, “frequently updated”, “periodically updated”, “updated periodically”, “updated annually”, “annually updated” or “living”.Each report meeting the previously mentioned characteristics and the subsequent publications of the same review will be included and treated as a single study (i.e. review /evidence synthesis), considering the initial publication as the baseline one and the subsequent publications as its updates. Nevertheless all review reports will be assessed independently in order to collect the data of interest (see data collection).. With this aim we will useEpistemonikos database as main source; this is a comprehensive database of systematic reviews and other types of evidence synthesis reports, maintained by screening multiple information sources to identify SRs and their included primary studies, including the Cochrane Database of Systematic Reviews, Pubmed/MEDLINE, EMBASE, CINAHL, PsycINFO, LILACS, DARE, HTA Database, Campbell database, JBI Database of Systematic Reviews and Implementation Reports and EPPI-Centre Evidence Library. This database has been validated, showing its completeness in collecting the published SRs and other type of evidence syntheses.The identification of the evidence synthesis of interest will be carried out through systematic and exhaustive searches in the biomedical databasesThe searches will cover from the inception date. No publication status or language restriction will be applied to the searches in Epistemonikos. The boolean literature search strategy that will be used is presented inWe will update the searches in Epistemonikos prior to the publication of this review, looking for updates to the already identified living evidence synthesis.Additional searches. In order to identify new articles or update reports that might have been missed in the electronic searches, we will manually search websites of the organizations reporting the living evidence synthesis identified in electronic searches and email the contact authors of all the included reviews to ask for publications of their updates, particularly when there is no a published update identified within a year from the last publication.  of the Epistemonikos Foundation. This platform has been validated as a repository for the COVID-19 showing to be a highly comprehensive source of evidence, where the duplicate references will be identified and eliminated by an automated process. A special algorithm comparing unique identifiers  and citation details  will be implemented to ensure updates of the same review will not be identified as duplicates of the original publication.Results from these searches will be automatically included in the Living Overview of Evidence (L.OVE) platformTwo researchers (AA and JB) will independently screen the search results based on the title and abstract and confirm eligibility according to the selection criteria. We will retrieve the full-text article of the references that meet the eligibility criteria or require further analysis, to decide on their inclusion. Disagreements will be solved by reaching a consensus between reviewers.As it was previously mentioned, each of the included articles and subsequent publications of the same review, arising from the “living evidence” updating process, will be linked and included as a single study (i.e. review /evidence synthesis). As part of this process we will identify the original publication, the subsequent publications and search manually for unpublished updates. In the case that the original publication was not identified as part of our search , we will run necessary searches to identify whether it is, using related references, authors names, or title words; if necessary, we will perform a manual search and contact the review authors. in order to identify the relevant methodological items to be collected. Based on this review, we developed a preliminary list of variables to be collected as part of this study that were later validated by the research group experts in the field.Five researchers trained in advance will extract data from all the included review reports; each report will be assessed by two professionals who will extract data independently using a specifically designed standardized form to collect the information of interest. This form has been developed on the basis of previous work done by our research team, that reviewed all methodological and guidance papers published up to July 2021 describing a “living evidence” methodologyThe final list of variables to be collected see includeschecklist for systematic reviews and NCCMT Quality Assessment Tool, for other review articles). Two independent authors will complete the assessment on the original publication (baseline review) and subsequent updated reports or publications. Disagreements will be solved by consensus. We will pay particular attention to changes in the methodological quality through publications of the same review. Results of this assessment will be presented in descriptive tables.To be able of identifying the methodological quality of the baseline reviews and any variations through its multiple updates, as part of the data collection we will assess the methodological quality of all included evidence synthesis reports using the appropriate instruments . We will present the results in tables, both for each review report and for the group of publications linked to the same review/evidence synthesis. Qualitative data  will be presented in tables.We will check the methodological issues reported by the authors against those in the list of variables that we previously defined based on the review of methodological articles.The aspects related to the updating of the reports, scientific publications or other forms used by authors to disseminate the review updates, will be collected and presented as qualitative information in summary tables, since this is one of the methodological aspects still to be defined in living evidence processes.If feasible, we will report the results in subgroups by the type of synthesis .PROSPERO registration. This protocol is registered under the accession number CRD42021248963Ethical considerations. As researchers will not access information that could lead to the identification of an individual participant, obtaining ethical approval was waived.Data sharing. All data related to the project will be available. Epistemonikos Foundation will grant access to data.The way in which authors are currently incorporating the living evidence approach into systematic reviews and other synthesis products is still unknown.This project will permit to identify, evaluate and summarise the methods and procedures that different groups are using to generate and keep the evidence “living”.One of the biggest challenges of setting up a “living evidence” process is to rapidly transfer the results of the updates to end-users, such as clinicians and other decisions makers. There are some proposals done in this regard so far but not a clear route to reach this goal. This project will identify the current practice and methods used by authors to disseminate the constant updates of the evidence synthesis as well as those aspects that will permit the living evidence authors to maintain informed their final users through its multiple updates.This study will provide information on the compliance of the current authors of the living evidence synthesis with the methodological standards proposed so far, which will serve to improve the living evidence synthesis reports, increase their transparency, as well as guide their potential evaluation.No data are associated with this article.Extended data10.17605/OSF.IO/27MECOpen Science Framework: LIVING EVIDENCE TO INFORM HEALTH DECISIONS. Registration DOIThis project contains the following extended data:Reporting guidelineshttps://osf.io/fm6ej/Open Science Framework: PRISMA-P checklist for “Methodological approaches for developing and reporting living evidence synthesis: a study protocol”Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).Data are available under the terms of the I recommend approval of the latest version.Is the study design appropriate for the research question?YesIs the rationale for, and objectives of, the study clearly described?YesAre sufficient details of the methods provided to allow replication by others?YesAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:NAI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. I have no further comments to make.Is the study design appropriate for the research question?NoIs the rationale for, and objectives of, the study clearly described?NoAre sufficient details of the methods provided to allow replication by others?NoAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:Systematic reviews and guideline developmentI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard. Methods for living reviews are evolving and a study to determine the current methods being used by review authors will be important as we move forward, in particular if compared to the variety of methods being proposed today. Below I have included a few suggestions that may improve the paper. I believe that this study is not a methodological review. My understanding of a methodological review is a review of studies that assess the effects of a method used in research (sometimes compared to another method), or association of a method with some outcome, and these effects or associations are pooled together across studies if possible . To me, instead, this paper is a survey of what methods are currently being used. This may explain why on Page 4, the reference to the  ‘intervention of interest’ does not seem to apply. If you change this to a survey, the PRISMA checklist/statement would not be used when reporting this paper. Since this study is about the methods for living reviews, I think it should be more broad. The information that will be extracted seems to focus mostly on the search methods, but there are other methods that are or could be affected when conducting a living review. I have mentioned a few below but I think the authors should explore the different methods that are currently being discussed in the literature and expand the data they will collect. For example, the authors could consider adding how the results of the search and screening are reported as there seems to be some research about different methods of reporting being used. Alternatively, the authors may decide not to gather this data and instead refer to the paper by Kahale 2021. There is also some literature about the statistical methods that could be used in living reviews (see Simmonds 2017). The Simmonds paper identifies many important methods that could be used. The authors have not indicated that they will collect data about different methods of statistical analyses and interpretation, but could. In addition, there is some question about the criteria to decide when re-analysis and a subsequent publication should occur when doing a living review . Data about if and how the authors of the reviews report these methodological decisions would likely be important to collect. It’s not clear to me why the methodological quality of the reviews are being assessed. How will this information be used? In addition, do the current tools actually address issues relevant to living reviews? Will these tools provide quality information relevant to a living review in particular? A minor comment: I understand that different types of reviews will be included, but the paper may be easier to follow if the living 'reviews' are not referred to as ‘studies’.References et al. Tailored PRISMA 2020 flow diagrams for living systematic reviews: a methodological survey and a proposal . F1000Research 2021, 10:192 (https://doi.org/10.12688/f1000research.51723.2) Kahale LA, Elkhoury R, El Mikati I  Simmonds M, Salanti G, McKenzie J, Elliott J; Living Systematic Review Network. Living systematic reviews: 3. Statistical methods for updating meta-analyses. J Clin Epidemiol. 2017 Nov; 91:38-46.Is the study design appropriate for the research question?NoIs the rationale for, and objectives of, the study clearly described?NoAre sufficient details of the methods provided to allow replication by others?NoAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:Systematic reviews and guideline developmentI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Dr. Santesso, we thank your careful reading of the manuscript and your constructive comments. We have taken them into account in order to improve and clarify the manuscript. Please find below a detailed point-by-point response to your comments. Comment 1 Methodological review vs methodological surveyI believe that this study is not a methodological review. My understanding of a methodological review is a review of studies that assess the effects of a method used in research (sometimes compared to another method), or association of a method with some outcome, and these effects or associations are pooled together across studies if possible . To me, instead, this paper is a survey of what methods are currently being used. This may explain why on Page 4, the reference to the ‘intervention of interest’ does not seem to apply. If you change this to a survey, the PRISMA checklist/statement would not be used when reporting this paper.Reply to comment 1 We have reviewed and is no clear nomenclature in biomedical literature for this type of study aimed to assess the methods used by others. Due to the lack of standardization between the terms “methodological survey”, “methodological review” or “meta-epidemiological study”, we decided to use “methodological study” rather than a “methodological review” to be informative and allow for appropriate indexing. A methodological study is defined as any study that describes or analyzes methods  in published (or unpublished) literature.  We have introduced changes in our protocol according to this type of study design, which includes changes in the title and the methods section of this manuscript (see lines 136-147).  Ref: Mbuagbaw, Lawrence & Lawson, Daeria & Puljak, Livia & Allison, David & Thabane, Lehana. (2020). A tutorial on methodological studies: The what, when, how and why. BMC Medical Research Methodology. 20. 226. 10.1186/s12874-020-01107-7.Comment 2 Exploring different methods of conducting a living review. Since this study is about the methods for living reviews, I think it should be broader. The information that will be extracted seems to focus mostly on the search methods, but there are other methods that are or could be affected when conducting a living review. I have mentioned a few below but I think the authors should explore the different methods that are currently being discussed in the literature and expand the data they will collect. For example, the authors could consider adding how the results of the search and screening are reported as there seems to be some research about different methods of reporting being used. Alternatively, the authors may decide not to gather this data and instead refer to the paper by Kahale 2021.Reply to comment 2 Prior to defining the variables to be collected, we conducted a review of methodological and guidance articles published up to June 2021, all the references you have mentioned but Kahale 2021, were included and reviewed, they were already listed previously as part of the protocol references . The publication by Kahale 2021 was published later of our initial review but is now included as part of references reviewed: Ref Nº13. Kahale L, Elkhoury R, El Mikati I, et al.: Tailored PRISMA 2020 flow diagrams for living systematic reviews: a methodological survey and a proposal. F1000Research. 2021; 10. Based on the previous work done by other authors, we defined the variables to be collected and exceed those related only to the search methods. This list already includes information about how results of the search and screening are reported, as we presented in tables 2 and 3. Nevertheless, taking into account your comments we have reviewed the list of variables and provided a better explanation of its operational definition  (see tables 2 and 3).  Comment 3 Data related statistical methods that could be used in living reviewsThere is also some literature about the statistical methods that could be used in living reviews (see Simmonds 2017). The Simmonds paper identifies many important methods that could be used. The authors have not indicated that they will collect data about different methods of statistical analyses and interpretation, but could. In addition, there is some question about the criteria to decide when re-analysis and a subsequent publication should occur when doing a living review . Data about if and how the authors of the reviews report these methodological decisions would likely be important to collect.Reply to comment 3 Even though the publication by Simmonds 2017 was included in our review of prior work done, we agree that still some variables related to statistical methods are needed. We have added new variables to collect specific information related to the statistical methods inspired in Simmonds 2017 work.See: “Data to be collected from the baseline report” in table 2- Planning for evidence monitoring /surveillance, and “Data to be collected from the updates” in table 2- Information about the integration of new evidence (NEI))Comment 4 The methodological quality of the reviews are being assessed It’s not clear to me why the methodological qualities of the reviews are being assessed. How will this information be used? In addition, do the current tools actually address issues relevant to living reviews? Will these tools provide quality information relevant to a living review in particular?Reply to comment 4 A living systematic review should derive from a reliable systematic review, the "baseline review". Our aim in conducting the methodological quality assessment of both, the baseline report and their subsequent updates, is to assess if the methodological quality is maintained, improved, or decreased through its multiple updates. We agree with you, the AMSTAR II checklist, as well as the other instruments we have proposed to use, are not addressing the relevant issues of living evidence synthesis or reviews. Even though we will use them for this assessment because they do address important quality issues that any systematic evidence synthesis should meet. We have improved the explanation of this procedure in the text: Lines 217-225. To be able of identifying the methodological quality of the baseline reviews and any variations through its multiple updates, as part of the data collection we will assess the methodological quality of all included evidence synthesis reports using the appropriate instruments . Two independent authors will complete the assessment on the original publication (baseline review) and subsequent updated reports or publications. Disagreements will solve by consensus. We will pay particular attention to changes in the methodological quality through publications of the same review. Results of this assessment will be presented as part of the descriptive data in tables.Comment 5. Reviews’ nomenclature A minor comment: I understand that different types of reviews will be included, but the paper may be easier to follow if the living 'reviews' are not referred to as ‘studies’.Reply to comment 5 We have changed the references from “study/ies”  to “review/s” throughout  the manuscript. The change was introduced early in the text as follows: Line 154 Each report previously mentioned and the subsequent publications of the same review will be included and treated as a single study (i.e. review /evidence synthesis).After this, we use “review” for referring to the included evidence synthesis or reviews. This is a really interesting project that can provide relevant added value in the realm of systematic reviews. The protocol draft is sound and well written. Please find below some suggestions to the authors:Search strategiesAn additional search using a highly sensitive search strategy will be performed on PubMed/MEDLINE, in order to compare results and be able to identify additional evidence synthesis reports not obtained from searches in Epistemonikos”. The draft reads as follows “ This is intended to validate Epistemonikos as a database for searches on living reviews, including systematic reviews, network meta-analyses and living overviews. Since the main database for searching is Epistemonikos, it would be interesting to elaborate a little more about its quality and previous validation. Many readers may not be familiar to this database.Assessment of the methodological quality  Authors will evaluate the quality of all included studies  using the AMSTAR II checklist and other appropriate instruments according to the type of study . Reference 21 in the draft is that of a previous version of the AMSTAR tool (published in 2007). Probably it would be better to swap the current reference 21 for the following: Shea B J, Reeves B C, Wells G, Thuku M, Hamel C, Moran J et al. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both BMJ 2017; 358 :j4008 doi:10.1136/bmj.j4008Did the review authors use a satisfactory technique for assessing the risk of bias (RoB) in individual studies that were included in the review?” An important limitation of the AMSTAR II tool is that the quality of individual studies in the meta-analysis is poorly evaluated. Domain 9 reads as follows: “ There are two possible answers to this question, namely: Partial Yes, must have assessed RoB fromunconcealed allocation, andlack of blinding of patients and assessors when assessing outcomes  For Yes, must also have assessed RoB from:allocation sequence that was not truly random, andselection of the reported result from among multiple measurements or analyses of a specified outcome Likewise, the NCCMT Quality Assessment Tool-Review provides a poor approach to the RoB assessment of individual studies in the review (described on Question 6 of the tool). Foraddressed, regardless the resulting quality of individual studies included. Furthermore, in both AMSTAR II and NCCMT tools, the score in Domain 9 and Q6, respectively, is obtained simply if information on allocation, blinding, etc., has been This is really poor approach to the RoB assessment of individual studies included in the reviews which is a key aspect for the reliability of published results. At present, the Cochrane collaboration is piloting its RoB2 tool. Ideally, RoB in the individual studies of the reviews should be re-assessed with the help of better tools like RoB2. If not possible, this should be stated in the protocol as a limitation of the LE systematic review.Additional information on Table 2. One of the variables included in Table 2 is the “Journal/Editorial Group/Publisher”. I would also include the “impact factor” in order to showcase the “visibility” of living evidence. Likewise, the “Journal/Editorial Group/Publisher” and “impact factor” of the last update could also be included in Table 3.Is the study design appropriate for the research question?YesIs the rationale for, and objectives of, the study clearly described?YesAre sufficient details of the methods provided to allow replication by others?YesAre the datasets clearly presented in a useable and accessible format?Not applicableReviewer Expertise:systematic reviews and pharmacoepidemiologyI confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Dr. Erviti, we thank your careful reading of the manuscript and your helpful comments and suggestions. Please find below our reply to your comments and suggestions. Comment 1 Search strategiesThe draft reads as follows “An additional search using a highly sensitive search strategy will be performed on PubMed/MEDLINE, in order to compare results and be able to identify additional evidence synthesis reports not obtained from searches in Epistemonikos”.This is intended to validate Epistemonikos as a database for searches on living reviews, including systematic reviews, network meta-analyses, and living overviews. Since the main database for searching is Epistemonikos, it would be interesting to elaborate a little more about its quality and previous validation. Many readers may not be familiar with this database. Reply to comment 1 We have decided not to carried out additional searches because Epistemonikos has been already validated for identification of any type of evidence syntheses. We have changed the paragraph and added a sentence with specific reference (reference  17). Lines 161-168: With this aim we will useEpistemonikos database as the main source; this is a comprehensive database of systematic reviews and other types of evidence synthesis reports, maintained by screening multiple information sources to identify SRs and their included primary studies, including the Cochrane Database of Systematic Reviews, Pubmed/MEDLINE, EMBASE, CINAHL, PsycINFO, LILACS, DARE, HTA Database, Campbell database, JBI Database of Systematic Reviews and Implementation Reports, EPPI-Centre Evidence Library [16]. This database has been validated, showing its completeness in collecting the published SRs and other type of evidence syntheses [17]*. *Reference 17: Rada, G., Pérez, D., Araya-Quintanilla, F. et al. Epistemonikos: a comprehensive database of systematic reviews for health decision-making. BMC Med Res Methodol 20, 286 (2020).https://doi.org/10.1186/s12874-020-01157-x  Comment 2 Assessment of the methodological qualityAuthors will evaluate the quality of all included studies  using the AMSTAR II checklist and other appropriate instruments according to the type of study . Reference 21 in the draft is that of a previous version of the AMSTAR tool (published in 2007). Probably it would be better to swap the current reference 21 for the following: (1) Shea B J, Reeves B C, Wells G, Thuku M, Hamel C, Moran J et al. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomized or non-randomised studies of healthcare interventions, or both BMJ 2017; 358 :j4008 doi:10.1136/bmj.j4008Reply to comment 2 We have updated the reference in the protocol according to your suggestion: Reference 22. Shea B J, Reeves B C, Wells G, Thuku M, Hamel C, Moran J et al. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both BMJ 2017; 358 :j4008 doi:10.1136/bmj.j4008Comment 3 Assessment of the methodological quality An important limitation of the AMSTAR II tool is that the quality of individual studies in the meta-analysis is poorly evaluated. Domain 9 reads as follows: “Did the review authors use a satisfactory technique for assessing the risk of bias (RoB) in individual studies that were included in the review?”There are two possible answers to this question, namely: For Partial Yes, must have assessed RoB fromunconcealed allocation, andlack of blinding of patients and assessors when assessing outcomes For Yes, must also have assessed RoB from:allocation sequence that was not truly random, andselection of the reported result from among multiple measurements or analyses of a specified outcomeLikewise, the NCCMT Quality Assessment Tool-Review provides a poor approach to the RoB assessment of individual studies in the review (described on Question 6 of the tool). Furthermore, in both AMSTAR II and NCCMT tools, the score in Domain 9 and Q6, respectively, is obtained simply if information on allocation, blinding, etc., has been addressed, regardless the resulting quality of individual studies included. This is really poor approach to the RoB assessment of individual studies included in the reviews which is a key aspect for the reliability of published results. At present, the Cochrane collaboration is piloting its RoB2 tool. Ideally, RoB in the individual studies of the reviews should be re-assessed with the help of better tools like RoB2. If not possible, this should be stated in the protocol as a limitation of the LE systematic review.Reply to comment 3 The goal of our analysis is to evaluate the methodological quality of the included SRs, from both the baseline one and their subsequent publications, but not the validity of the conclusions. We will then assess quality over time through the subsequent updates.Comment 4. Additional information on Table 2. One of the variables included in Table 2 is the “Journal/Editorial Group/Publisher”. I would also include the “impact factor” in order to showcase the “visibility” of living evidence. Likewise, the “Journal/Editorial Group/Publisher” and “impact factor” of the last update could also be included in Table 3. Reply to comment 4 We have added the additional information regarding the “impact factor” on journal publication Living evidence products in table 2. We believe this variable will help to summarize the scope of the journal and add value to our descriptive analysis.


To search, evaluate, and summarize the best evidence of intermittent pneumatic compression devices to prevent venous thromboembolism in trauma patients. S” evidence model, including guidelines, clinical decision making, evidence summary, expert consensus, and systematic reviews. The retrieval time limit was from the establishment of the database to August 31, 2022. Two researchers independently evaluated the quality of the literature, extracted evidence, and summarized evidence.  Evidence retrieval was conducted from top to bottom according to the “6 A total of 140 studies were obtained in the literature retrieval, and 50 studies were obtained after rechecking and reading the title and abstract. After combining the inclusion and exclusion criteria, 19 studies were finally included. Among them, there were 12 guidelines, 1 clinical decision making, 1 evidence summary, 1 expert consensus, and 4 systematic reviews. The 27 best pieces of evidence were summarized from the four dimensions of pretreatment evaluation, contraindications and applicable conditions, treatment strategies, training, and patient education.  This study summarized the evidence of using an intermittent pneumatic compression device to prevent venous thromboembolism in trauma patients and provided the basis for scientific and effective standardized management of mechanical thromboembolism prevention. When applying evidence, it is necessary to combine clinical practice and patient wishes and select evidence pertinent to improving the effectiveness of intermittent pneumatic compression devices in preventing venous thromboembolism. In addition, compliance with the clinical application of IPC is relatively low, so we should start from two aspects before the application of evidence. We should not only increase the number of IPCs but also strengthen the training of VTE prevention knowledge and practical skills of medical staff to provide good health education for patients and their families to improve compliance with the clinical application of IPC. Trauma has become one of the main problems affecting health , and itsP (population): trauma patients, age ≥18 years old; Intervention I: IPC; P : hospital managers and medical staff; Outcome index O (outcome): DVT incidence, pulmonary embolism incidence, VTE incidence; Evidence application site S (setting): hospital ; Type of evidence T (type of evidence): guidelines, systematic reviews, evidence summary, clinical decision making, expert consensus/opinion/position statement, and original research closely related to evidence.We used the PIPOST model developed by JBI as a tool to construct evidence-based questions , that is∗” OR “polytrauma” OR “wound∗” OR “injury∗” OR “multiple injury”) AND  AND , UpToDate (4), Joanna Briggs Institute Evidence-Based Health Care Center Database (JBI) (1), National Guidelines Clearinghouse (NGC) (1), National Institute for Health and Care Excellence (NICE) Registered Nurses' Association of Ontario (RNAO) (0), Scottish Intercollegiate Guidelines Network (SIGN) (1), Guidelines International Network (GIN) (1), EBSCO (0), Cochrane Library (1), PubMed (9), Embase (0), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (0), American College of Chest Physicians (ACCP) (0), and European Society for Vascular Surgery (ESVS) (0). The retrieval time was from the establishment of the database to August 31, 2022. Literature inclusion criteria were as follows: the subjects were trauma inpatients aged ≥18 years old; the content of the literature involved the evaluation, intervention, or management of VTE prevention by using intermittent air pressure therapy devices in trauma patients; and evidence types included guidelines, clinical decision making, evidence summary, expert consensus, systematic reviews, and original research related to evidence. Exclusion criteria were as follows: (1) documents with duplicate publications, incomplete information, and inability to obtain full text; (2) document types mainly include plans, drafts, reports, and abstracts; and (3) research that did not pass document quality evaluation.We used “traumaThe quality evaluation of the guidelines adopts the 2012 version of the Appraisal of Guidelines for Research and Evaluation (AGREE II) . The scaA recommendation (strong recommendation) and level B recommendation (weak recommendation)  . AccordiTwo researchers who have received evidence-based medicine training will conduct independent evaluations according to the corresponding standards of different document types. If the evaluation results cannot be agreed upon, the third evidence-based medicine expert can discuss until reaching a consensus. When the conclusions of evidence from different sources are in conflict, the inclusion principle followed in this paper is evidence-based evidence first, high-quality evidence first, and the latest published literature first.A total of 140 studies were obtained in the literature retrieval, and 50 studies were obtained after rechecking and reading the title and abstract. After combining the inclusion and exclusion criteria, 19 studies were finally included. Among them, there were 12 guidelines, 1 clinical decision making, 1 evidence summary, 1 expert consensus, and 4 systematic reviews (see In this study, the correlation coefficients within different groups was used to test the consistency of the quality evaluation of the guidelines. A total of 12 guidelines , 18–26 wThis study included 1 clinical decision from UpToDate  and 1 suThis study included one expert consensus. The reference is from tThis study included four systematic reviews –32, one This study systematically evaluated and analyzed 19 studies, comprehensively sorted out the evidence, and finally formed four dimensions of pretreatment evaluation, taboos and applicable conditions, treatment strategies, training, and patient education, with 27 best pieces of evidence .Trauma patients are high-risk patients with VTE. All hospitalized trauma patients should undergo VTE risk assessment and bleeding risk assessment, which is helpful to further grade the risk of thrombosis to give corresponding thromboprophylactic measures . At presAt present, routine VTE prevention methods include basic prevention, drug prevention, and mechanical prevention. The multimodal approach combining IPC and drug prevention is the most effective in reducing venous thromboembolism . For patAt present, the effectiveness of IPC in preventing VTE has been recognized, but its compliance in clinical application is not high. Based on an observational study, the overall compliance with IPC treatment is only 29% , 41. TheTraumatic patients have a tendency of thrombosis within 24 hours after injury, and their blood is also in a hypercoagulable state. Generally, this tendency is most obvious approximately 5 days after injury, and it begins to decline 14 days after injury. Therefore, if there is no contraindication, preventive measures should be started as soon as possible . GeneralIn clinical practice, low compliance with IPC treatment is related not only to the above patient factors but also to medical staff factors. A lack of VTE-related training for medical staff will directly affect the effect of IPC mechanical prevention , and strVTE is one of the more common and preventable complications of trauma patients during hospitalization. As a strategy for thrombosis prevention, IPC is an important choice. This study uses scientific research methods to summarize the 27 best studies for IPC to prevent VTE in trauma patients, providing an evidence-based basis for the implementation of clinical IPC. We also want to see the update of IPC equipment. Wall et al.  used a n


Considerable evidence supports the role of present-moment attention, a central feature of mindfulness, in subjective wellbeing maintenance and enhancement. Yet it is not clear why such a relation exists. This study examined the genetic and environmental contributions of present-moment attention to subjective wellbeing. Consistent with the “generalist genes hypothesis” and prior evidence, we hypothesized that presence and subjective wellbeing would show a substantial genetic correlation and smaller environmental correlation. Using a large epidemiological sample of healthy 16-year-old twins in the United Kingdom (N = 1136 monozygotic (MZ) and dizygotic (DZ) twin pairs), genetic overlap was found between presence and the cognitive component of subjective wellbeing (life satisfaction), and to a lesser extent, the affective component of subjective wellbeing . The non-shared environmental overlap between these constructs was substantial. This study provides the first evidence known to us showing that present-centered attention, a primary component of mindfulness, has both genetic and environmental overlap with subjective wellbeing. The findings have implications for understanding mechanisms by which presence is associated with positive emotions and life satisfaction, and suggest, pending additional research, that mindfulness-based interventions to enhance wellbeing may be best suited to those with a genetic propensity toward mindful presence. Along with interest in such effects has been a search for conditions supportive of wellbeing, and several theories have been proposed in this regard2, among them “mental state theories,” which highlight the role of states of attention in wellbeing. Flow theory3 and mindfulness theory  are exemplars of such theories, and evidence supports the role of present-moment attention, or attention to current events and experiences, in subjective wellbeing maintenance and enhancement5. Yet it is not clear why such a relation exists, and the present study was designed to examine the genetic and environmental contributions of present-moment attention (“presence”) to subjective wellbeing.Scientific and popular interest in wellbeing has flourished in the past two decades, spurred in part by evidence that wellbeing is associated with a range of positive biopsychosocial outcomes, including mental health, positive social relations, physical health, and longevity5 and the Act with Awareness subscale of the Five Factor Mindfulness Inventory6 is phenotypically associated with higher subjective wellbeing7. Randomized trials of mindfulness training centrally feature instruction in focused, present-centered attention. They have shown pre-post intervention enhancements in subjective wellbeing, particularly increased positive affect and reduced negative affect . Conversely, correlational and experimental research on mind-wandering has shown it to be associated with higher negative over positive affect10. Likewise, rumination has well-established associations with certain forms of negative affect . Finally, both rumination and negative affect are moderately, inversely correlated with presence .Subjective wellbeing is commonly considered a combination of cognitive evaluation, reflected in satisfaction with one’s life, and a predominance of positive over negative affective states over time. Presence is a central feature in various conceptualizations of mindfulness. It is reflected in a tendency to pay attention to what is currently taking place within and around oneself, rather than to be immersed in thoughts about the past or future, as in mind wandering, rumination, and other forms of cognitive time travel. Self-reported presence, as measured by instruments such as the Mindful Attention Awareness Scale12). But there is reason to hypothesize that mindfulness, and in particular its key component of presence, has genetic overlap with wellbeing. Previous research has found that both present-centered attention and subjective wellbeing have substantial genetic influence. For example, a twin study by Waszczuk et al.13 estimated that presence, as assessed with the Mindful Attention Awareness Scale, was 32% attributable to genetic influence. Other research has estimated 30–50% genetic influence on subjective wellbeing . Recent large-sample genome-wide association studies have identified a number of polymorphisms associated with subjective wellbeing . While no research has shown genetic links between presence and subjective wellbeing, Waszczuk et al.13 found genetic correlations of 0.52 and 0.53 between Mindful Attention Awareness Scale scores and depressive and anxiety sensitivity symptoms, respectively. Depressive symptoms in particular have been inversely correlated with subjective wellbeing  and both phenotypes form part of a “wellbeing spectrum” with substantial genetic intercorrelations .Theoretical accounts have posited several psychological processes through which mindfulness enhances wellbeing, including attention regulation, emotion regulation, and altered self-perceptions . Thus, environmental influences may better explain the relation between presence and subjective wellbeing. By examining the contribution of both genetic and environmental factors in the association between presence and subjective wellbeing, the present investigation will promote our understanding of the biological and behavioral processes that link these traits13. Also, a better understanding of how individual differences in present-centered attention are related to subjective wellbeing can lead to more precise training to enhance wellbeing.Together this evidence concerning presence and wellbeing lends support to the “generalist genes hypothesis”The primary goal of this study was to examine the genetic overlap between presence and subjective wellbeing, using a large epidemiological sample of healthy 16-year-old twins in the United Kingdom. Consistent with the generalist genes hypothesis and prior evidence, we hypothesized that presence and subjective wellbeing would show a substantial genetic correlation and smaller environmental correlation. Our first aim was to test the phenotypic correlation between presence and subjective wellbeing. Our second aim was to examine the genetic and environmental influences on presence and subjective wellbeing variables individually. Third, we investigated what proportion of the expected phenotypic association between presence and subjective wellbeing was explained by genetic (relative to shared and nonshared environment) influences.21 for recruitment details). The present study focuses on twins born between 1994 and 1996. Data for this study were collected in 2011, when the twins were approximately 16 years old on average. The parent study was approved by the Kings College London Research Ethics Committee (PNM/09/10-104). The study was performed in accordance with relevant guidelines and regulations. Informed consent was obtained from parents and all participating adolescents. Zygosity was established using parent-report questionnaires of physical similarity, a method estimated to be 95% accurate relative to DNA testing22. Where zygosity was unclear, DNA testing was conducted. Participants were excluded if they experienced severe pre- or perinatal complications, if they had a severe medical condition , or if sex or zygosity were unclear. The sample for analyses consisted of 1136 monozygotic (MZ) and dizygotic (DZ) twin pairs ; 429 MZ pairs  and 707 DZ pairs .Adolescent participants came from the population-representative Twins Early Development Study (TEDS), which comprises over 10,000 twin pairs born in England and Wales  with response options ranging from “almost always” to “almost never.” Previous research has shown that the scale items correlate highly with items phrased oppositely, as attentiveness5. This lends credibility to the scale as a measure of presence, rather than simply a lack thereof. Responses were averaged to provide trait presence scores; higher scores reflect higher presence. Sample Cronbach’s alpha was acceptably high (α = 0.75).Present-centered attention was measured using a brief (5-item), item response theory-validated version24 assesses subjective perceptions of general happiness . The 5-item Brief Multidimensional Student Life Satisfaction Scale25 assesses satisfaction with one’s life in five domains: family, school, friends, self, and living environment (example item: “I would describe my satisfaction with my family life as:” with response options ranging from “terrible” to “delighted”26). Responses were summed to create a total life satisfaction score (sample α = 85). Large-scale studies report that subjective wellbeing is a latent factor that comprises affect and life satisfaction in both adults27 and children28. To assess subjective wellbeing at a global level in supplementary analyses, Subjective Happiness Scale scores (“happiness”) and Brief Multidimensional Student Life Satisfaction Scale scores (“life satisfaction”) were averaged together, as they used the same 1–7 Likert scaling.Two validated scales were administered that together assessed subjective wellbeing. The 4-item Subjective Happiness Scalehttps://osf.io/6fd7m). Analyses were based on the twin method29, which compares the degree of similarity between MZ twins (sharing 100% of their genetic variations) and DZ twins . These relative differences in within-pair correlations allow estimations of the influences caused by additive genetic, shared environmental, and nonshared environmental influences on a trait or the covariation between traits. Where correlations are higher for MZ twins than for DZ twins, genetic influences are inferred to be acting (A). Within-pair similarity that is not due to genetic factors is accounted for by shared environmental influences (C), which contribute to the resemblance between family members. C is evident when DZ correlations are more than half MZ correlations. Nonshared environment (E) accounts for factors that create individual differences between siblings. These are estimated from within-pair differences between MZ twins. E also includes measurement error.The study analyses were preregistered on OSF (30 within the R package (www.R-project.org) to examine Aims 1–3. Aim 1 concerned the phenotypic correlations (rph) between presence and subjective wellbeing (happiness and life satisfaction separately). Aims 2 and 3 concerned the genetic and environmental bases of these associations. A constrained saturated model was first used to calculate twin and cross-twin cross-trait correlations. Twin correlations are within-twin pair, within-trait correlations; specifically, correlations within MZ pairs (rMZ) and within DZ pairs (rDZ) were computed for presence, happiness, and life satisfaction separately. Cross-twin cross-trait correlations were computed by correlating a trait in one twin with another trait in the co-twin . Twin and cross-twin cross-trait correlations permit a first look at how individual differences and associations between them are due to genetic (A), shared environmental (C), and nonshared environmental (E) factors.Twin model fitting was performed in OpenMx31 to address aims 2 and 3 of this study. Specifically, rph, A, C, and E influences on presence and the subjective wellbeing variables were estimated, as well as the genetic and environmental correlations between these variables . These latter correlations indicate the degree of genetic and  environmental overlap between two traits. The proportion of the phenotypic correlations (rph) due to genetic or environmental factors was also estimated. For example, using the nomenclature shown in Fig. rph between presence and life satisfaction can be estimated as rAa11a22, divided by rph. All variables were normally distributed so no transformations were applied.Building on the initial results revealed by twin and cross-twin cross-trait correlations, a multivariate correlated factors model Fig.  was fitt32. All models were fitted using full information maximum likelihood to account for missing data. The core fit statistic was minus twice the log likelihood (− 2LL) of the observations. This is not an overall measure of fit, but provides a relative measure of fit, since differences in − 2LL between models are distributed as χ2. Therefore, to examine the overall fit of the genetic model we compared the − 2LL to that of a saturated model . The fit of each submodel was assessed by χ2 difference tests, Akaike’s and Bayesian’s information criterion ) with lower χ2 values, and more negative AIC and BIC values suggesting a better fit. If the difference between the AIC of two models was less than 10, the more parsimonious model was selected33. For all analyses, we also compared models with fewer parameters to the full A, C, and E correlated factors solution. To assess the precision of parameter estimates, 95% confidence intervals (CIs) were obtained. CIs that include zero indicate that an estimate is nonsignificant. CIs that do not overlap indicate that two estimates differ significantly.Following standard procedures, the variables were regressed for sexThe Institutional Review Board of Kings College London approved all procedures performed in this study involving human participants.All participants provided informed consent prior to participation in the study.rp = 0.18 and 0.24 respectively). The difference in the magnitude of these correlations was significant, p = 0.016. The MZ twin correlations were larger than the DZ correlations ; and (b) that genetic influence on this trait is best interpreted as additive . The MZ twin correlations between presence and both life satisfaction  was significantly larger than that between presence and happiness (rA = 0.22), p < 0.001. Estimates of the proportion of rph due to A and E indicate that shared genetic influences explained approximately half the phenotypic correlation of presence with happiness  but unknown are the bases for this association. The current study is the first known to us to examine the genetic and environmental etiologies of the association between self-reported dispositional presence and subjective wellbeing. We hypothesized that presence and wellbeing would show a substantial genetic correlation and smaller environmental correlation, in accord with the generalist genes hypothesis17 as well as prior evidence. Genetic overlap was found between presence and the cognitive component of subjective wellbeing (life satisfaction), and to a lesser extent, the affective component of subjective wellbeing . The environmental overlap between these constructs was substantial, however.Over the past several decades there has been a burgeoning interest in mindfulness, of which present-centered attention (presence) is theorized to be a key component5) rather than with adolescents. Also, this study used a brief version of the Mindful Attention Awareness Scale. While the internal consistency of the measure was adequate, it is possible that higher phenotypic correlations might be obtained with the full version of the scale. For example, Brown et al.35 found higher correlations between the full Mindful Attention Awareness Scale and both affect and life satisfaction in a large sample of normative adolescents (mean age = 16.73 years). Thus the results obtained here concerning genetic and environmental influences on presence, subjective wellbeing variables, and their associations might be somewhat measure-dependent.We first showed that, as in other research over the years, there was a phenotypic association between presence and the subjective wellbeing variables . These correlations were smaller than those seen in previous studies, but most prior research on this topic has been conducted with adults  and functional magnetic resonance imaging . Emotion regulation, in turn, is an important underpinning for subjective wellbeing46. Mind-wandering also links presence47 and wellbeing10, and mind-wandering has been associated with default mode network activity in the brain48. If both presence and subjective wellbeing are associated with reduced mind-wandering and default mode network activity in the brain, then these psychological and neural factors may also, along with emotion regulation, represent mechanisms of the genetic link between presence and wellbeing.There is growing interest in understanding the mechanisms that link presence and wellbeing. The shared genetic etiology of these two traits begs a question concerning the neurobiological mechanisms linking them. This topic has not been investigated directly, but research has found links between presence, as measured by the Mindful Attention Awareness Scale and other, related measures, and neural markers of emotion regulation, assessed both through encephalography , as appears to be true for SWB14. The question of how mindfulness or presence develops is, we argue, an important one to better understand how to foster this adaptive disposition.Consistent with previous reports using the TEDS databaseThis study had a large sample, permitting genetically informed analyses. It was limited in several ways however. First, the sample was composed largely of White participants, limiting the conclusions to this population. The results may also not generalize to adult populations since genetic and environmental influences on psychological traits can change with age. Research is needed to examine whether the results found here concerning the genetics of present-centered attention and the genetic and nonshared environmental origins of the associations between presence and wellbeing traits extend to non-White adolescent populations and to diverse populations of adults. Second, the reliance on self-report measures introduced the possibility of shared method variance, which may have inflated parameter estimates. In particular, method variance, if it existed, would inflate non-shared environmental correlations (rather than genetic correlations). If different methods to measure the study variables were to be used, the non-shared environmental correlations might be smaller than those reported here.51. However recent research using network analysis indicated that two of the most commonly used mindfulness scales  actually reflect more well-established constructs concerning executive attention and other psychological phenomena51. Thus the simpler concept of presence may represent a more appropriate level of investigation of day-to-day attention, which mindfulness scales in part purport to assess. Additionally, the Mindful Attention Awareness Scale has been shown to be associated with neural activation and functional connectivity in and between attention regions of the brain that have been associated with mindfulness-based interventions as well45. This lends credibility to the use of the Mindful Attention Awareness Scale to assess a component of mindfulness.A third limitation is that the study cannot inform about mindfulness, since present-centered attention is considered an element of mindfulness, not the entire phenomenon49.A fourth limitation is inherent to twin (and family) studies of genetic influence. Studies using twin designs have assumptions and limitations concerning equal environments, gene-environment correlation, and gene x environment interaction (GxE) effects. The implication is that this study’s findings concerning genetic influences on presence, subjective wellbeing variables, and their associations could include interactions between genes and shared environmentsFinally, it is unclear why the genetic presence—life satisfaction overlap was considerably larger than that between presence and happiness; we speculate that the two former measures tap quite stable characteristics relative to the happiness measure, which may be more subject to circumstantial influences.only benefit those with a particular genetic makeup; while genes may be influential, they are not typically deterministic.In conclusion, this study provides the first evidence known to us showing that a component of mindfulness, namely present-centered attention, has both genetic and non-shared environmental overlap with subjective wellbeing. This has implications for our understanding of the mechanisms by which presence is associated with positive emotions and life satisfaction. On the environmental side of the equation, it could be that positive or negative life experiences might impact both presence and wellbeing. On the genetic side, consideration of genetic influences may inform mindfulness-based interventions to enhance wellbeing; such interventions may be best suited to those with an inherent propensity toward mindful presence. Yet is highly unlikely that that such interventions will 52. The derived polygenic scores, wherein individual genetic effects are summed together, could be used to more closely examine genetic overlap between wellbeing and presence phenotypes in future research.Among next steps in this line of work, research is needed to identify specific genes associated with presence. Genome-wide association studies (GWAS), have not been conducted to examine associations between measured genetic variants and present-centered attention, or mindfulness, but GWAS has been performed to identify genes associated with subjective wellbeingSupplementary Tables.


Successful HIV-1 prevention and therapy will require broad and potent coverage of within-host and global viral diversity. Broadly neutralizing antibody (bNAb) combination and multispecific therapeutics provide an opportunity to meet this challenge due to the complementary activity of individual antibody components. Here, we review the principles and applications of this concept.The Antibody Mediated Prevention (AMP) trials have demonstrated the high bar for neutralization potency and breadth that bNAb-mediated prevention modalities will need to achieve to have a meaningful impact on the HIV-1 epidemic. Additional clinical studies have recently shown that an even higher bar may be required for therapeutic inhibition of the diverse within-host quasispecies present in viremic and aviremic people with HIV-1 (PWH). We discuss how the complementarity of bNAbs in terms of neutralization profiles, resistance mutations and coverage of within-host quasispecies may overcome these stringent requirements and lead to effective bNAb combination or multispecific antibody based prophylactic and therapeutic strategies.The design of next-generation bNAb-based combination or multispecific therapeutics for the prevention and/or treatment of HIV-1 infection will need to leverage the complementarity of component bNAbs to maximize the potency and breadth that will be required for clinical success. To achieve ≥90% protection, predicted serum ID80 titers (PT80) of ≥ 200 would be required, which translates to VRC01 neutralizing titers of 80% inhibitory concentration (IC80) ≤0.1 μg/ml against infecting viral isolates assuming average pharmacokinetic concentration of VRC01 from the 30 mg/kg dose group in the AMP trials [9▪▪,de novo, but this is alarming regardless since it suggests a high propensity of resistance may exist in people living with HIV to at least some individual bNAbs. In the setting of 3BNC117 and 10–1074 combination therapy in viremic participants, this phenomenon was even more accentuated; most participants had viral loads return to near baseline levels following transient declines post-bNAb infusions, and the rebound viral population exhibited resistance to both bNAbs [Several recent clinical trials studying bNAb-based prevention and therapeutic strategies have underscored the high bar of neutralization potency and breadth that will be required for success otection ▪▪. To acials 9▪▪,. Second,ials 9▪▪,▪ and NCTials 9▪▪,▪). Whileials 9▪▪,▪. It is th bNAbs ▪. Howeve80 titers) to VRC07–523LS was found in a single participant. A combined analysis of this study together with prior studies involving the dual combination of 3BNC117 and 10–1074 and monotherapy with either 3BNC117 or VRC01 suggested that on average PT80 titers of >1000 would be needed to control viremia (or more precisely to avoid viremic rebound), which would translate to single or combination neutralizing titers of IC80 < 0.02 μg/ml using the above average pharmacokinetic concentration from the AMP trials. Together, these clinical studies outline that potent neutralization of virtually all circulating strains of HIV-1 will be required for clinical success. Although to date no single bNAb can meet this stringent requirement, combinations of bNAbs or multispecific antibodies have the potential to do so [▪▪,This phenomenon was further highlighted by a third phase 1 clinical trial that evaluated viremic control after a single dose of a triple bNAb combination of VRC07–523LS (anti-CD4bs), PGT121 (anti-V3-glycan) and PGDM1400 (anti-V2-apex) NCT03205917) ▪. In thi17 ▪. In do so ▪▪,▪.in vitro neutralization against genetically diverse global isolates compared to each component bNAb alone [80 titers and significant overlap in commonly sensitive or commonly resistant viruses   and N6/P9  and N6bNAbs isolated from multiple PWH have been found to recurrently target distinct epitopes on the Env trimer, with CD4bs, V2-apex and V3-glycan (“high mannose patch”) epitopes among the most frequently targeted . It is eThe independence of bNAb-resistance mutations has further been demonstrated in clinical studies of bNAb combinations in which the evolution of resistance mutations to one bNAb did not confer resistance to other bNAbs in the combination, and multiple independent resistance mutations were required to confer resistance to multiple bNAbs. For example, three out of four viremic participants treated with the dual combination of 3BNC117 and 10–1074 developed neutralization resistance only to 10–1074 , and rebAnother potential mechanism for partial bNAb resistance can be posttranslational modifications on Env such as glycosylation heterogeneity or conformational heterogeneity in genetically identical virions. This can result in a fraction of clonal virions exhibiting resistance to bNAbs, and is often observed as incomplete neutralization curve plateaus or persistent fractions ,24,25▪. in vivo potency requirements as outlined above.The challenges that must be overcome for clinical success of bNAb-based prevention and therapeutic regimens are further amplified by the issue of HIV-1 diversity that arises from both the heterogeneity of within-host quasispecies in each person living with HIV-1 as well as regional differences in the genetic makeup of locally circulating strains  . Not onlPassive immunization studies in PWH have demonstrated that resistance to any single bNAb is readily observed in the viral quasispecies at baseline (i.e. before bNAb therapy), even with the relatively low number of participants enrolled in these trials. Across the 3BNC117 and 10–1074 combination trials described above, 13 out of 34 participants had fully resistant viruses at baseline to one or both bNAbs ▪. In theAlthough individual bNAb resistance is commonplace, resistance to multiple bNAbs may be more rare. Only two participants in the dual bNAb combination trials ▪,12▪ andThe advantage of redundant bNAb coverage, i.e. multiple bNAbs in the combination simultaneously covering within-host diversity, in therapeutic settings is clearly demonstrated by combination bNAb clinical trials, where participants harboring baseline viruses potently neutralized by two or three bNAbs typically exhibit prolonged viral suppression or viral control as compared to those participants with viruses sensitive to only a single bNAb ▪,12▪,13▪Recent clinical studies have underscored the challenges associated with the use of single or combination bNAbs for the prevention and/or treatment of HIV-1 infection. To address these stringent requirements, the different levels of complementarity among bNAbs for improved potency and breadth need to be carefully considered in the design and development of combination strategies that can overcome the barriers for clinical success. While in this review we have focused on conventional bNAb neutralization effector activity, the same principles of bNAb complementarity will also apply for inhibition of cell-cell spread and nonneutralizing Fc-mediated effector functions.None.Bill & Melinda Gates Foundation Collaboration for AIDS Vaccine Discovery (INV-036842).There are no conflicts of interest.