PDL1/PDL2/PLGRKT (8.2%), MYC/PVT1 (6.1%), MACROD2 (4.1%) and KLF5/KLF12 regions (4.1%). We detected the overexpression of PDL1 and MYC upon integration by gene expression analysis. In conclusion, we identified recurrent targeting of several cancer genes such as PDL1 and MYC upon HPV integration, suggesting a role of altered gene expression by HPV integration during HNSCC carcinogenesis.A prevalence of around 26% of human papillomavirus (HPV) in head and neck squamous cell carcinoma (HNSCC) has been previously reported. HPV induced oncogenesis mainly involving E6 and E7 viral oncoproteins. In some cases, HPV viral DNA has been detected to integrate with the host genome and possibly contributes to carcinogenesis by affecting the gene expression. We retrospectively assessed HPV integration sites and signatures in 80 HPV positive patients with HNSCC, by using a double capture‐HPV method followed by next‐generation Sequencing. We detected HPV16 in 90% of the analyzed cohort and confirmed five previously described mechanistic signatures of HPV integration . Our results suggested that HPV remained episomal in 38.8% of the cases or was integrated/mixed in the remaining 61.2% of patients with HNSCC. We showed a lack of association of HPV genomic signatures to tumour and patient characteristics, as well as patient survival. Similar to other HPV associated cancers, low HPV copy number was associated with worse prognosis. We identified 267 HPV‐human junctions scattered on most chromosomes. Remarkably, we observed four recurrent integration regions:  Five previously described mechanistic signatures of human papillomavirus (HPV) integration  are confirmed in our head and neck squamous cell carcinoma cohort. Two hundred sixty‐seven HPV‐human junctions scattered on most chromosomes are reported. HNSCC is the seventh most common cancer worldwide HNSCC main risk factors are alcohol and tobacco use and human papillomavirus (HPV) infection. The overall HPV prevalence in HNSCC is 26% and reaches up to 80–90% for oropharyngeal squamous cell carcinomas (OSCC) E6 and E7 viral oncogenes when HPV remains as an episome or if integration happens outside a gene. Then, E6 and E7 oncoproteins expression respectively disrupts p53 and pRb tumour suppressors. Whereas, integration into or near a human cancer related gene can affect the gene expression and directly contribute to carcinogenesis via chromosome instability, gene disruption, or regional amplifications within the cellular genome HPV is a small double‐strand DNA virus of approximately 8000 base pairs. More than 200 genotypes have been identified, among which 13 high risk HPVs are recognized as carcinogens by the International Agency for Research on Cancer. During the oncogenic process, the viral genome can be maintained as extrachromosomal nuclear episomes and/or it can be integrated into the host genome We previously developed the HPV double capture method followed by next‐generation sequencing (NGS) to: (a) precisely determine HPV genotypes, (b) characterize the HPV sequence , (c) analyze the viral‐host DNA junctions, (d) quantify the HPV copy number per sample and (e) assess the sites and signatures of HPV integration into the human genome Several studies across different tumour localizations focused on HPV integration and its impact on gene expression and immune microenvironment modulation, but much remains to be confirmed , 17.Nonintegrated HPV has been previously reported to exert oncogenic effects while maintaining status as viral circular DNA in oropharynx squamous cell carcinoma (OPSCC) MYC, TMEM49, FANCC and RAD51B genes. Conversely to cervical cancer, few studies documented in the literature report HPV integration sites in HNSCC. Parfenov et al. revealed some similarities in HNSCC, with HPV integration events targeting RAD51B, NR4A2 and TP63  but01) Fig.  [16].3.4E6 and E7 oncogenes. Deletions were observed in E1, E2, E5, L1 or L2 viral genes (data not shown).All patients displaying HPV integration exhibited deletion in some viral genes, albeit systematically retaining 3.5Both tumour and lymph node samples at diagnosis were available for two patients. HPV16 was the viral genotype in both cases. The signatures were the same at both sites (one patient with EPI and one with MJ‐SC). The Table 3.6n = 7/29, 23.3% in the EPI population vs. n = 4/46, 8.7% in the HPV integrated population, P = 0.07) and for the absence of lymphovascular invasion . We also found a trend for an association between the HPV signature and HPV copy number (P = 0.06). The association is statistically significant between 2J signature and low HPV copy number , as compared to the “not 2J” population  (P = 0.020).Table 3.7To validate suspected HPV integration into the human genome, we designed primers with one of them being derived from the human genome at the potential site of integration and the other against HPV sequences suspected of being near the site of integration within the HPV genome. The primers were designed 200–400 bp away from the detected integration sites based on the NGS reads.6 bp from the integration site). The protein coding genes represent 141/267 genes and are enriched in genes related to cancer (based on 685 OncoKB genes) as compared to the total number of genes in a human genome (based on 19 982 GENCODE protein coding genes).Integration in the human genome was observed scattered on all chromosomes except on the small chromosome 21 as represented in Figure P = 1.06 × 10‐6).In fact, OncoKB cancer related genes represent 11.3% (16/141) of the protein coding genes found near insertion sites, as compared to 3.4% of the entire human genome (685/19 982) , whereas 22.4% of patients only harbored intergenic integrations . HPV‐Human DNA recombinations within a single sample (≥3 junctions) were detected for 15/49 HPV integrated patients in our cohort. PCR and sequence analyses confirmed the 7 junctions observed in sample R14 (Data not shown).The number of HPV integration sites per tumour corresponds to 16.8 (267/49) in our series of HNSCC, while it is 5.5 for anal n = 4/49, 8.2%) was the 9p24.1 region. It contains two important immune checkpoint genes: PDL1, PDL2 and PLGRKT  had integration near MYC and PVT1 in the 8q24.21 region . Finally, two patients  had integration in the KLF5/KLF12 containing region.Remarkably, we found four recurrent integration regions. The first chromosomal region with frequent integration  or DFS (P = 0.87)  and DFS (P = 0.07)  Fig. . There w07) Fig. . No asso3.9PDL1/PDL2/PLGRKT region, and for two (R654 and R661) of the three patients with HPV integration in the MYC/PVT1 region. Figure PDL1, PDL2 and PLGRKT containing region showed overexpression of PDL1 (but not of PDL2 and PLGRKT)  is overexpressed in the two patients with HPV integration in the MYC/PVT1 region, as compared to the expression in the 42 other HNSCC tumours  of the four patients with HPV integration in the r two R65 and R661KT) Fig. . R295 isDL1 Fig. . MYC . There were trends towards an association between 2J signature and higher expression (near two fold as compared to the two other groups) of several genes CD20 (marker of B lymphocytes), CD163 (marker of M2 macrophages), ITGAM (marker of myeloid‐derived suppressor cells), as well as IL8 (neutrophils chemoattractant cytokine), OX40L (a major immune checkpoint), VIM (marker of EMT) and APOBEC3H but not APOBEC3A and APOBEC3B. Of note, there was no association between HPV genomic signature and well‐known markers of cell proliferation such as MKI6 or CCND1.We tested the possible association between HPV genomic signatures and the expression of various immune‐related genes in our cohort of 44 HNSCC patients with available RNA Table . We obse4PDL1 region, MYC and PVT1 region, MACROD2 region and in KLF5/KLF12 region). PDL1 and MYC were overexpressed upon integration.In the present study, we used the robust and sensitive double capture method, followed by NGS on 80 patients with HPV positive HNSCC. HPV16 was the main detected genotype. No HPV co‐infection was noted. We did not find any HPV18 infection. We confirmed the five previously described mechanistic HPV signatures with distribution close to the one observed in ASCC but different from the one described in CC. No correlation was established between HPV genomic signature s and known clinico‐biologic prognostic factors. A low HPV copy number tended to be associated with worse prognostic and with the 2J signature. We identified 267 HPV‐human chromosome junction sequences scattered on all chromosomes with four integration hotspot regions ((p). Further studies using long read sequencing such as Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT) are needed to (a) assess the mechanistic of HPV insertion and junction‐related signatures and (b) to differentiate between hybrid human–virus ecDNA and chromosomal HPV DNA [The HPV16 predominance and the absence of HPV18 could be explained by the high proportion of oropharyngeal tumour in our samples. HPV18 is known to be rare in HPV‐positive oropharyngeal SCCs compared with other sites   HPV DNA , 29 in oP = 0.07). A recent study on HPV‐positive oropharyngeal tumours used digital droplet PCR to assess the copy number and confirmed that high viral copy number is associated with better clinical outcomes P = 0.06). The association is statistically significant between 2J signature and low HPV copy number when compared to the “not 2J” population (P = 0.020).HPV genomic signatures seem to have no impact on outcome or response to treatment. Previous studies found that HNSCC harbouring HPV integration had worse survival than those with HPV remaining in an episomic state Two patients with matched samples (primary tumour and synchronous lymph nodes) displayed the same signatures at both sites. This finding supports the data on HPV clonal evolution during HPV induced carcinogenesis PDL1, PDL2 and PLGRKT. PDL1 and PDL2 encode for the two ligands for the PD‐1 immune inhibiting checkpoint, which plays a role in the negative regulation of the adaptive immune response. PD‐L1 or PD‐L2 are upregulated in many human tumours, including HNSCCs PDL1 (CD274) amplification  showing aberrant expression in multiple human cancer types. PVT1 is implicated in the malignant progression of HNSCC and represents a potential biomarker and therapeutic target in HNSCC (p1). It is known to interact with its neighbor MYC, resulting in MYC upregulation MYC gene in CC [MYC region display the highest MYC expression, which may be explained by DNA focal gain  in the present study.This work provides new insights into the role of HPV integration in HNSCC and opens new avenues regarding the biological interplay between the virus and HNSCC immune microenvironment. Our study has several limitations: First of all, the small sample size might have hindered reaching statistical significance when correlating to clinical outcome or when assessing the relationship between HPV genomic signatures and immune‐related gene expressions analyses. A second limitation is the long inclusion period (1997–2017) when cancer treatments have consistently evolved over the past twenty years. Dedicated functional analyses are needed to better evaluate HPV integration consequences on immune microenvironment. Overall, prospective clinical studies on HPV‐positive HNSCC patients need to be conducted to demonstrate the antitumour efficacy of targeting agents in light of the molecular alterations identified as companion biomarkers . PDL1 and MYC genes were overexpressed upon HPV integration. Our hotspot genes have a direct role in carcinogenesis with different mechanisms: immunomodulation, loss of tumor suppressor, activation of oncogenes and upregulation of transcription factors. HPV induced HNSCC carcinogenesis is more complex than first described. It relies on three actors: the virus, the host and the immune system.For many years, HPV oncogenic potential was only attributed to the viral oncoproteins E6 and E7, but recent studies highlights that HPV integration is an oncogenic event All other authors report no conflict of interest.Conception and design: IB, CLT and, MK. Development of methodology: IB, CLT, NS, SL and AN. Acquisition of data: CC, JPD, MK, JM, AM, ES, PS, AS, SV, JK, SI, SL, JMP and ADV. Analysis and interpretation of data : MD, JM, NS, SV, EG, AH and JMP. Writing, review and/or revision of the manuscript: JM, IB, CLT, MK, CD, LLC, CL and RR. Study supervision: IB and MK.https://publons.com/publon/10.1002/1878‐0261.13219.The peer review history for this article is available at Fig. S1A. Samples analysis description and proportion of episomal, mixed and integrated HPV samples.Click here for additional data file.Fig. S1B. Variations of the depth of coverage at the E2 and E6 genes loci according to viral integration status.Click here for additional data file.Fig. S2. Distribution of HPV genomic signatures in patients with anal squamous cell carcinoma (A) or cervical cancer (B) and comparison to the signature observed in HNSCC. Chi‐square test, P value for global comparison of EPI group vs. MJ‐SC vs. MJ‐CL vs. 2J‐COL group vs. 2J‐NL vs. 2J‐UN between HNSCC vs. ASCC P = 0.94 and HNSCC vs. CC P < 0.0001. 2J‐COL: two hybrid colinear junctions; 2J‐NL: two hybrid nonlinear junctions; 2J‐UN: two hybrid junctions with a lost junction; EPI: episomal; MJ‐CL: multiple hybrid junctions clustered in one locus; MJ‐SC: multiple hybrid junctions scattered at distinct loci.Click here for additional data file.Fig. S3. HPV integration breakpoints in the chromosomal region 8q24.21 in three patients with HNSCC. We represented PVT1 9 exons. Each color corresponds to a patient: R654, 619 and R661. Each Arrow is a breakpoint position. 9ptel indicates the telomere and Cen the centromere. The numbers indicate the genomic positions.Click here for additional data file.Fig. S4. Survival curves representing the association between disease free survival (A–C) or overall survival (D–F) and HPV status in head and neck squamous cell carcinoma. Survival curves representing the association between disease free survival (G and H) or overall survival (I and J) and HPV status in oropharynx patients. No statistical difference was observed in terms of DFS (A–C) or OS (D–F) in patients with episomal, integrated and mixed HPV statuses. These results were confirmed in the oropharynx patients (G–J). Log‐rank test was used.Click here for additional data file.Fig. S5. Association with survivals in 80 patients with head and neck squamous cell carcinoma: (A) Association between disease free survival and HPV genomic signatures. (B) Association between disease free survival and HPV copy number. (C) Association between overall survival and HPV genomic signatures. (D) Association between overall survival and HPV copy number. EPI: episomal, 2J: two junction, MJ: multiple junctions, NS: non‐significant. Log‐rank test was used.Click here for additional data file.Fig. S6. Examples of focal gain or amplification of HPV integrated CD274 (A) and MYC (B) genes. Each arrow represents a focal gain or an amplification.Click here for additional data file.Table S1. Clonal breakpoints found in the primary tumour and in the lymph nodes of the same patient at diagnosis.Click here for additional data file.Table S2. HPV integration sites in human chromosomes of 49 HNSCC patients.Click here for additional data file.Table S3. Clonal breakpoints found in the primary tumour and in the lymph nodes of a same patient at diagnosis.Click here for additional data file.Table S4. Association between HPV genomic signatures and clinical and pathological characteristics of 80 patients with HPV‐positive head and neck squamous cell carcinoma.Click here for additional data file.Table S5. HPV integration sites in human chromosomes of 49 HNSCC patients.Click here for additional data file.Table S6. Associations between HPV genomic signatures and mRNA expression levels of immune‐related genes, EMT genes, cell proliferation genes and APOBEC genes.Click here for additional data file.


Recent trends in the incidence of lung cancer have been reported despite the decreasing rate of smoking. Lung cancer is ranked among the top causes of cancer-related deaths. The ratio of adenocarcinoma to squamous cell carcinoma, as well as the ratio of women to men, is still increasing. Human papillomavirus (HPV) has been discovered in lung cancer tissues and blood specimens, particularly in Eastern countries. However, the association between HPV infection and lung adenocarcinoma remains unclear.This population-based cohort study was conducted using data from Taiwan's single-payer national health insurance and cancer registry databases. Data on HPV infection, cancer, sex, age, comorbidities, urbanization, and occupation were collected. The cumulative incidence rates were generated using Kaplan–Meier curves and log-rank tests. COX regression analysis was used to estimate the hazard ratios of factors associated with cancer occurrence. We used data from 2007 and 2015. The cases were matched with sex and age in a 1:2 manner with 939,874 HPV+ and 1,879,748 HPV– individuals, respectively.The adjusted hazard ratios [95% confidence interval (CI)] for HPV infection in all lung cancers were 1.539 (1.436–1.649), male lung cancer 1.434 (1.312–1.566), female lung cancer 1.742 (1.557–1.948), squamous cell carcinoma (SCC) 1.092 (0.903–1.320), male SCC 1.092 (0.903–1.320), female SCC 0.949 (0.773–1.164), adenocarcinoma 1.714 (1.572–1.870), male adenocarcinoma 1.646 (1.458–1.858), and female adenocarcinoma 1.646 (1.458–1.858). The highest adjusted hazard ratio for lung cancer was chronic obstructive pulmonary disease (COPD) 1.799 (1.613–2.007), followed by male sex 1.567 (1.451–6.863) and HPV infection. The highest adjusted hazard ratio for adenocarcinoma was HPV infection 1.714 (1.572–1.870), followed by COPD 1.300 (1.102–1.533), and for SCC, male sex 5.645 (4.43–3.37), followed by COPD 2.528 (2.002–3.192).Our study showed that HPV infection was associated with the occurrence of adenocarcinoma of the lung in both men and women but was not associated with SCC of the lung. Helicobacter pylori, and human papillomavirus (HPV), which contribute to 20–25% of all globally registered cancer cases , lung cancer (ICD-9: 162), cervical cancer (ICD-9: 180. X), and head and neck cancer (ICD-9: 195. X) were chosen as the standards since HPV infection is known to induce cervical and head and neck cancers . All patient data from the National Health Insurance Research Dataset were de-identified; therefore, the requirement for signed informed consent was waived.t-test for numerical data. The relative risk of cancer was calculated using a multiple Cox regression model. The cumulative incidence rates of cancer were generated using Kaplan–Meier curves and tested by the long-tank test.SAS 9.4  was used for statistical analyses in this study. For the design of the cohort study, the index date was identified as the starting point and the incidences of cancer from the index date to 31 December 2015 were included. Patients with HPV before 2008 or those with cancer before the diagnosis of HPV were excluded. The non-infected cases were matched with HPV-infected cases according to age, sex, and index date with structured query language (SQL) in a 2:1 manner. Patients with cancer onset before the index date were excluded. In this study, comparisons were made between HPV-infected and non-HPV-infected individuals. Demographic data were compared using the chi-square test for categorical data and Student's p = 1.0,000) (p < 0.0001). Officers and laborers had more HPV infections than farmers or unemployed workers did (p < 0.0001). As for comorbidities, the incidence of HPV infection was positively correlated with hyperlipidemia, ischemic heart disease, hypertension, peptic ulcer, gastrointestinal bleeding, chronic kidney disease, and COPD but not with diabetes mellitus.During the period of 2007–2017, 1,103,771 people tested positive for HPV, yielding an incidence rate of 4.2% . Among t1.0,000) . A positp < 0.01), with an incidence rate of 21.86/100,000 person-years in the HPV positive individuals and an incidence rate of 14.32/100,000 person-years in HPV-negative individuals. The HR for indiscriminate lung cancer was 1.539 , with an incidence rate of 39.44/100,000 person-years for individuals with HPV and an incidence rate of 25.54/100,000 person-years for individuals without HPV. Among all lung cancer individuals, men had an HR of 1.539  between HPV-positive and HPV-negative individuals, with an incidence rate of 47.47/100,000 person-years for HPV-positive individuals and an incidence rate of 33.40/100,000 person-years for HPV-negative individuals. In comparison, women had an HR of 1.742 (1.557–1.948), with an incidence of 31.57/100,000 person-years for HPV-positive individuals and an incidence rate of 17.83/100,000 person-years for HPV-negative individuals. The incidence rate was higher in HPV-positive than in HPV-negative cervical cancer (p < 0.001)  , head an< 0.001) , and lun< 0.001) .p = 0.6,886) in the male population and 1.540  in the female population, which was almost significant  in the male population and 1.812  in the female population  was higher than that in the HPV-negative population  among both men and women  . In addipulation . Stratifp-value (p). The contributing factors of lung cancer included HPV infection, sex, age, occupation, and other comorbidities . Similarly, male individuals had a higher risk of lung cancer compared to their female counterparts . The aHR of lung cancer was also proportional to the stratified age. With age 20–40 years as a reference, an aHR of 0.046  was observed among individuals <20 years of age, an aHR of 12.679  was observed among individuals aged 40 and 60 years, an aHR of 45.477  was observed among individuals between the ages of 60 and 80 years, and an aHR of 73.521  was observed among individuals above the age of 80 years. Furthermore, individuals covered by the insurance of the farmers' and fishermen's unions had greater risk  compared to individuals with laborers' union insurance. Among the common comorbidities listed in p < 0.0,001), COPD , and peptic ulcer  were at a greater risk of lung cancer than those without the respective comorbidities. However, the results were dissimilar between cancer cell types.The factors associated with lung cancer were determined by COX regression analysis, demonstrated with the adjusted hazard ratio (aHR), 95% confidence interval (CI), and bidities . Individp < 0.001) compared to their female counterparts. An aHR was also proportional to age. With age 20–40 as a reference, an aHR of 26.152  was observed between the ages of 40 and 60 years, an aHR of 155.166  between the ages of 60 and 80 years, and an aHR of 267.473  above the age of 80 years. The degree of urbanization, on a scale of 1–7 was also a contributing factor. With 1 as a reference, the degree of urbanization of 3 had an aHR of 1.579  and 7 had an aHR of 1.792 . Additionally, aHR varied across insurance plans. Compared to the insurance covered by the Laborers' Union, the insurance covered by the government  showed a significantly higher aHR, farmers' union , and low-income household subsidies . Among the common comorbidities listed, COPD had an aHR of 2.528  with the highest aHR among all comorbidities.In individuals with squamous cell carcinoma, sex, age, urbanization, insurance coverage, and comorbidities were contributing factors . Male inp < 0.0,001) compared to non-HPV individuals, which was the highest among all factors, except age. An aHR was also proportional to age. With age 20–40 years as a reference, an aHR of 0.016 was seen in individuals below the age of 20, an aHR of 26.12.803  between the ages of 40 and 60 years, an aHR of 37.078  between the ages of 60 and 80 years, and an aHR of 51.748  above the age of 80 years. The degree of urbanization also varied with the survival rate of individuals with adenocarcinoma. On a scale of 1–7, degree 2 , degree 3 , and degree 4  had significantly lower aHR. Furthermore, individuals covered by the insurance of the Farmers' Union had an aHR of 1.182  compared to Laborers' Union. Among the common comorbidities, hypertension , abnormal liver function , COPD , and peptic ulcer  all exhibited higher rates.Significant causes of adenocarcinoma included HPV infection, age, urbanization, insurance coverage, and comorbidities . HPV-infp < 0.0,001) with HPV-negative counterparts as a reference. Compared to the age of 20–40 years, however, the maximum aHR was found at the age of 40–60 years , unlike the case in all lung cancer. In terms of insurance coverage, except for those covered by the government that had a lower aHR of 0.720 , cervical cancer individuals covered by all other insurance plans had a relatively higher aHR. Furthermore, renal failure was the main contributor to comorbidities, with an aHR of 2.725 .The contributing factors analyzed in indiscriminate lung cancer, squamous cell carcinoma, and adenocarcinoma individuals were similar to those of cervical cancer, including HPV infection, age, insurance coverage, and comorbidities . The aHRIn this study, we utilized a nation-based cohort study to investigate the important etiological role of HPV in lung adenocarcinoma. Our study found that HPV was associated with adenocarcinoma of the lung in both sexes in Taiwan, with a stronger association in the female population, whereas SCC occurred more frequently in men with COPD.6 people in 2011 and 43.5/106 people in 2014. In contrast, the standard female death rate increased and stabilized, with 12.0/106 people in 1981, 17.3/106 people in 1996, 17.5/106 people in 2001, 16.5/106 people in 2011, and 15.3/106 people in 2019. Before 1986, cervical cancer was the leading cause of death in the female population, followed by lung cancer, and lung cancer became the leading cause of death after 1986. The standard incidence rate of lung cancer in women was 24.8/106 people in 2011 and 28.3/106 people in 2014  pathway -(IL-17) pathway. Further studies suggested that p53 is regulated not only by E6 and E7 but also by E1 and E2 may also be involved  pathway . The red pathway . In addiinvolved . E5, a linvolved .Even though oropharyngeal and cervical cancers are recognized as the same oncogenic sexual transmission diseases and both are squamous cell epithelium, the pathways of oncogenesis are still different . We propThe data in our study were gathered from the National Insurance Database and Cancer Registry Database. However, details of the small incidence subtype, such as small cell and large cell lung cancers, were not provided in the database due to privacy protection policies. One of the main limitations of this study was the unrecognizable subtype and location of HPV. The data on cervical cancer and head and neck cancer were included as the standard of comparison to augment the validity of this study since the study of the HPV association of the two cancers was well established. Similarly, data supporting the association between diabetes mellitus and HPV were also included as the standard of comparison . NotablyAlthough the presence of HPV in lung cancer is a possibility, large-scale full virus subtype tissue screening is required to clarify the role of HPV in various subtypes of lung cancer, such as small cell lung cancer and neuroendocrine cell lung cancers. Furthermore, a study of the virology types of lung cancer to investigate the subtype of HPV in different lung cancers is needed, since most current studies only focus on types 16 and 18. Hence, more pathophysiological studies on other types of HPV are required.To increase the validity of the study, further population studies for small cell lung cancer are required by collecting a larger database of small and large cell cancers owing to the limited dataset on small cell lung cancer. Another limitation is the distinction between high- and low-risk HPV, as this study included mostly viral warts, unspecific plantar warts, and condyloma accumulates. In addition, the HPV-infected population in this study may be underestimated because individuals with subclinical HPV infection are unlikely to visit clinics, which is a natural limitation of the study population.Further study designs may include investigation of HPV distribution within the bodies of HPV-infected individuals. The study of the oncogenic mechanisms of adenocarcinoma and squamous cell carcinoma of the lung is also needed because of the different pathways across different HPV and cancer subtypes. For instance, the incidence of HPV-infected lung cancer continues to rise despite the decline of CIS in cervical pre-cancer incidence from 2008 to 2012 for women aged 18–20 years in the United States due to effective vaccination . VaccinaThis is the first epidemiological study demonstrating that HPV infection was associated with the occurrence of lung adenocarcinoma, whereas squamous cell carcinoma was mostly associated with COPD. Further validation is warranted to delineate whether there is a causal relationship between HPV infection and lung adenocarcinoma, or simply coexistence.The original contributions presented in the study are included in the article/The studies involving human participants were reviewed and approved by Chung Shan Medical University Hospital IRB. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.Conception or design of the work, data analysis, and interpretation: J-YH and FL. Data collection and approval of the manuscript: J-YH, CL, ST, and FL. Drafting the article: CL. Critical revision of the article: ST and FL. All authors contributed to the article and approved the submitted version.This study was funded by the Chung Shan Medical University Hospital CSH-2019-C-005. The English editing and Article Processing Charge are funded by Tungs' Taichung MetroHarbor Hospital TTMHH-C1110072.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The licensure of the first HPV vaccine was in 2006 and it took nearly a decade for the vaccine to be introduced in LIMCs. At the end of 2021, only 19 African countries had introduced the HPV vaccine in their national immunization programme . FurtherIn this editorial, we reflect on the key findings from four articles we guest edited for publication in the Research Topic “Advances in adolescent vaccination programs in Low- and Middle-Income Countries (LMICs): A focus on HPV vaccination capacity strengthening”. Our reflections are on three core and related areas all covered in the published articles: vaccine hesitancy, vaccination coverage, and operational challenges related to the delivery of HPV vaccines in LMICs.Haddison et al. reported nearly half (50%) of vaccinators being skeptical about HPV vaccination. Although the article reported findings from a small sample size (n = 24) of vaccinators in one of the country's districts, negative perceptions of HPV vaccination among the healthcare workers have been reported in many other settings. In many LMICs, healthcare workers are the trusted sources of information related to vaccines and immunization by the caregivers and the public. Therefore, negative perceptions of HPV vaccination by healthcare workers can result to low confidence toward the vaccine by the adolescents which in turn slows the momentum of HPV vaccination programmes. In South Africa, Khosa et al. administered a questionnaire that captured the 5C items to assess HPV vaccine hesitancy among caregivers with girls eligible for vaccination in one of the country's districts with <70% HPV vaccination coverage. The HPV vaccination programme in South Africa was initiated in 2014 at a national level through school-based delivery strategy. The Khosa et al. study reported that nearly 50% of caregivers pointed to factors related to vaccine hesitancy as the barriers to vaccinating their eligible girls. The factors in the 5C model that were found prevalent among the caregivers were: confidence, complacency, constraints, and collective responsibility. Another study in South Africa also pointed out that HPV vaccine hesitancy was observed in caregivers of girls attending private schools (In Cameroon, an article by rly half 0% of vacAmponsah-Dacosta et al. reviewed the challenges and opportunities for the HPV vaccination programme in South Africa. The review reports a contrast of >90% coverage observed during the piloting of the programme to a trend of declining HPV vaccination coverage of around 80% in the first year of national rollout and then, as low as around 40% in some districts as the programme matures. The review points to several reasons as potential contributors to the trend in declining HPV vaccination coverage in South Africa: inadequate reminder strategies, poor tracking and targeted follow up for those missing the second dose, weakening social mobilization efforts over time, and inadequate refresher training for vaccinators prior to rolling out the second round of vaccinations. Locally relevant advocacy and communication strategies are needed to address these barriers.Low confidence and skepticism toward HPV vaccination by healthcare workers, caregivers and adolescents will lead to suboptimal vaccination coverage. Karanja-Chege. Among the challenges reported in the review was lack of a reliable estimate for the target number of girls eligible for vaccination, negative sentiments about the HPV vaccines by influential sectors, as well as suboptimal knowledge on the benefits of the vaccination programme by key stakeholders. In South Africa, Amponsah-Dacosta et al. reported challenges related to the supply- and demand-side of the HPV vaccination programme. Supply side challenges include stock availability, costs as well as resources required for delivery of the vaccines. The demand side encompass issues related to vaccine confidence as well as convenient access to the vaccines. Addressing these challenges and taking the lessons learnt forward will be critical in laying a strong foundation for incorporating future adolescent vaccination programmes in LMICs.For many LMICs, adolescent vaccination was non-existent before HPV vaccine introduction. Operational challenges to HPV vaccine introduction in Kenya were reported in the review published by Adolescents, caregivers, healthcare workers, teachers, and the governments are all key stakeholders to advancing the HPV vaccination programmes in LMICs. Therefore, in settings where there is negative perceptions and suboptimal confidence among some of these key stakeholders, public health authorities should promptly act using effective evidence-based interventions to address the concerns of the caregivers and healthcare workers. A possible intervention is to conduct activities, including advocacy and communication strategies, aimed at improving knowledge and addressing low confidence and skepticism toward HPV vaccines. Such activities should be tailor made to the different target groups. For example, HPV vaccination workshops organized in Eastern and Southern Africa contributed to improved knowledge and sharing experiences on HPV vaccination programmes in the region . The worEmerging evidence points to a possibility of using a single rather than two dose HPV vaccination schedule . AdditioAll authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


This study examines challenges experienced during COVID-19 vaccination efforts, facilitating factors that increased vaccination, and lessons learned from healthcare providers and housing program staff who delivered healthcare and services to Veterans experiencing homelessness during the SARS-CoV-2 pandemic. Qualitative, semi-structured interviews were conducted with seven transitional housing program staff in northern California, southern California, Florida, Iowa, Kentucky, Massachusetts, and New Jersey (January-April 2021) and six primary care providers serving Veterans experiencing homelessness, four from clinics in California and two from a clinic in North Dakota (July-August 2021). Interviews were transcribed and analyzed using a rapid analysis approach. COVID-19 vaccination rates were between 40 and 60% among Veterans who received care from the primary care providers and between 20 and 90% among Veterans who were enrolled in the transitional housing programs. Barriers that providers and housing staff encountered when getting Veterans vaccinated for COVID-19 included lack of eligibility, the vaccine appointment scheduling process, transportation and communication challenges, Veterans’ distrust in the government, vaccine mandates, and vaccine hesitancy among organization staff. Recommendations to increase COVID-19 vaccine uptake included making vaccination more convenient, using trusted sources such as homeless program staff or Veteran peers to provide educational information about the safety and efficacy of COVID-19 vaccines, and encouraging rather than mandating vaccination. These lessons will enable entities providing care to people experiencing homelessness to develop more effective policies and educational campaigns to improve vaccine acceptance and uptake among this vulnerable population. Vaccination for COVID-19 is the most recommended public health measure for reducing the likelihood of severe illness or death from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and controlling the pandemic , 4. For Previous research has found that having multiple primary care visits and being enrolled in housing programs were significantly associated with COVID-19 vaccination uptake among unhoused Veterans, likely due to convenient access to care and having trusted relationships with service providers . FurtherThe study population included individuals who were employed at either (a) a U.S. Department of Veterans Affairs’ (VA) Homeless Patient Aligned Care Team (HPACT) or (b) a non-profit organization that is funded by the VA’s Grant and Per Diem (GPD) program. HPACT is a multi-disciplinary care model with clinics located in VA medical centers (VAMCs), community-based outpatient clinics (CBOCs), and community resource and referral centers  across the country. HPACTs consist of primary care providers, nurses, social workers, and mental health counselors who provide medical care, case management, housing and social services, community referrals, and substance use and mental health treatment . GPD orgThe study team conducted qualitative, semi-structured, sixty-minute telephone interviews with six HPACT providers  in California  and North Dakota , as well as seven GPD organization staff (four leaders and three case managers) in northern California (N.CA), southern California (S.CA), Florida (FL), Iowa (IA), Kentucky (KY), Massachusetts (MA), and New Jersey (NJ). Sites were recruited through a self-selected convenience sample and were chosen for their program size and geographic variability. Interviews with GPD staff occurred between January and April 2021 and interviews with HPACT providers occurred between July and August 2021. Study participants were asked about their experience providing care/services during COVID-19; vaccination rates among their population; measures taken to encourage COVID-19 vaccination; challenges faced in getting their Veterans vaccinated; Veterans’ attitudes regarding COVID-19 vaccination and the pandemic; and suggestions to increase vaccine uptake. Interviews were audio recorded, transcribed, and analyzed using the rapid analysis approach , 15–17. The nine HPACT and GPD programs in this study varied in size and Veteran patient population. The HPACT program in CA is one of the largest in the country and consists of 13 teams located within two VAMCs and one CBOC and serves approximately 2,600 Veterans. The four CA HPACT providers interviewed represented three clinical teams from one VAMC and the CBOC and served a combined total of 1,052 Veteran patients. The HPACT in ND is one of the smallest and newest programs, is within a CRRC, and served 110 Veterans at the time of the interviews. The GPD programs were all male only facilities with a total of 152 Veteran clients. The largest program, NJ, served 62 Veterans at the time of the interview while the smallest program, IA, served five.Three themes emerged from the qualitative interviews with HPACT providers and GPD program staff: (1) COVID-19 vaccination rates and processes; (2) challenges to vaccinating Veterans for COVID-19; (3) facilitators to COVID-19 vaccination and suggestions to increase COVID-19 vaccine uptake.Table CA HPACT utilized a local clinical dashboard to track COVID-19 vaccination numbers in the 13 clinics. The dashboard included both vaccinations within the VA and data from the California Immunization Registry (CAIR) , which iND HPACT did not have a local data dashboard but rather pulled VAMC-level vaccination rates from VHA Support Service Center’s (VSSC) COVID-19 Vaccine Tracker. Based on their internal clinic records, the study participants estimated that around 60% of their Veterans were vaccinated for COVID-19 as of 8/31/2021.At the time of the GPD staff interviews in early 2021, Veteran residents of the sites in NJ, N.CA, S.CA, KY, and IA had to make appointments at their VAMC to receive a COVID-19 vaccine. GPD staff in NJ and N.CA worked with VA staff to schedule appointments for Veterans. The S.CA respondent noted that the VA was contacting Veterans to schedule appointments. Both the FL and MA GPD arranged for clinical teams from the VA and a local pharmacy, respectively, to come vaccinate Veterans onsite. At both sites, Veterans who were unable to get vaccinated onsite could make appointments at their VAMC.HPACT providers cited that appointments were required for the first several months of the vaccine rollout; however, Veterans were able to walk-in and get vaccinated at the VA without appointments by summer 2021. CA providers at the VAMC noted that the COVID-19 vaccine could be administered near the HPACT clinic until May 2021, but later, Veterans had to walk to the main medical building to get vaccinated. Both appointment and walk-in processes required close coordination across the nursing, pharmacy, and scheduling teams. Veterans in ND could not be vaccinated at the HPACT clinic and typically had to travel to the main VAMC to receive a COVID-19 vaccine by appointment or walk-in. However, providers hosted two “vaccination blitzes” in the ND HPACT clinic in early February 2021 (see Facilitators to COVID-19 Vaccination for further detail).Respondents in HPACT and GPD programs cited organizational and individual-level challenges to getting Veterans vaccinated for COVID-19, see Table “We’re healthcare providers. I’ve got 16 staff. So, far, none of them have been vaccinated… And I’ve had two staff test positive... I have written congressmen. I have tried to e-mail the [VAMC] director. I have tried to go to Washington and e-mail the VA there. And I’ve talked to the Health Department… and this is the story I get: You’re not VA employees, even though you contract with them, so they don’t care about you…They don’t care if we get [COVID-19] from the [Veterans]. They just want to make sure that we help them… So, that’s my big frustration, and that’s why I call them the forgotten healthcare providers.” (FL GPD)GPD staff in IA and NJ expressed that lack of availability was initially a major barrier to rapidly vaccinating Veterans. The state of Iowa did not prioritize persons experiencing homelessness during the initial vaccine rollout and the respondent conveyed frustration at the lengthy wait time. In addition, most of the Veteran residents in IA were not eligible for VA healthcare, so they were unable to get the vaccine at the VA in early 2021 For CA HPACT clinicians, the appointment scheduling process was a major challenge before walk-in vaccination was available to Veterans. According to a HPACT respondent, neither HPACT nurses nor HPACT scheduling clerks were given permission to schedule vaccine appointments for patients; instead, a “return to clinic” order had to be issued by a primary care provider and then a scheduling clerk from a regular PACT clinic could schedule an appointment. This frustrated the vaccination efforts:Well probably 50% of the Veterans we serve aren’t located in the [city] area, they’re located in highly rural areas, and getting the vaccines out to the remote clinics, and we even have some clinics that are located in what’s still considered ‘frontier’ areas… It was a huge logistical effort to have the vaccines there, the staff there to deliver the vaccines, to care for people post-vaccine, yeah, it was a big logistical effort to make sure that happened...” (ND HPACT2)“HPACT providers in CA and ND cited transportation barriers in the early days of the COVID-19 vaccine rollout. COVID-19 vaccines were initially only offered at the main VAMCs, so patients receiving care at a CBOC or CRRC had to travel to the main campus, which was inconvenient and intimidating for most HPACT Veterans. Additionally, the VA shuttle between clinics in CA was discontinued during the height of the pandemic to minimize exposure risk. ND providers also noted challenges getting the COVID-19 vaccines to rural CBOCs:Respondents in HPACT and GPD identified communication challenges regarding COVID-19 vaccine availability. One CA HPACT provider believed that the VAMC did not effectively announce to VA staff and Veteran patients when and where vaccines were available. A NJ GPD staff member also stated that the VAMC did not give sufficient advance notice of vaccine availability to get Veteran residents signed up and arrange transport to the VAMC. Further, miscommunication between CA HPACT providers and local GPDs about which COVID-19 tests were required for GPD program entry exacerbated workload challenges for HPACT providers.“We have some who are like oh I’m gonna do it… I’ve just been busy with work. Or I’m gonna do it, I’ve just been depressed…. Or they’re going through the mental health stuff. Or they’re struggling with their addiction. So it’s not a priority for them. Because they’re distracted by these other things.” (N.CA GPD)Providers in both the HPACT clinics and GPD organizations noted that Veterans themselves likely did not experience many logistical barriers to receiving a COVID-19 vaccine since there were so many resources available to them. However, they cited various personal challenges hindering vaccination. For example, N.CA and NJ GPD staff mentioned that many Veterans have jobs or other competing priorities that may inhibit vaccine uptake:Participants in both HPACT and GPD cited Veterans’ distrust and cynicism as a barrier to COVID-19 vaccination. One HPACT provider in CA noticed that patients who were skeptical of other vaccines were also refusing the COVID-19 vaccine and that many of his Veterans cited the Tuskegee experiments as their reasons for distrusting vaccination. Two respondents, one from the HPACT clinic in CA and another from a GPD in NJ, noted that the younger Veterans, particularly those from the Operation Enduring Freedom/Operation Iraqi Freedom (OEF/OIF) generation , were more distrustful of the government and the VA, and thus more resistant to COVID-19 vaccination.“power struggle dynamic” for Veterans, exacerbating their distrust of the vaccine and cause them to “dig in” deeper in their opposition to vaccination. Instead, they suggested that trusted sources should encourage vaccination:“What I think I have seen that’s been more effective is when there’s more privileges allowed to those who have been vaccinated… Our GPD provider here in [city] has not mandated the vaccine yet… in my opinion it’s easier to work with Veterans through their case manager, through their trusted health provider to educate them about getting vaccines, rather than trying to force it.” (ND HPACT2)HPACT providers and GPD staff had differing views on the topic of mandating the vaccine. Some CA HPACT providers thought a mandate would help facilitate vaccine uptake, believing that if GPD programs or prospective employers made vaccination mandatory, more Veterans would get vaccinated. However, one ND provider opined that a vaccine mandate would create a “I have made the decision that… I will never make it mandatory for clients. That’s way too much of a barrier for our clients that already have a world full of barriers on their shoulders. And we are here to break down those and not set up more and requiring a vaccination… I’m not gonna put that barrier on our clients.” (IA GPD)At the time GPD staff were interviewed, vaccine mandates were not being considered a requirement for admission to transitional housing. Only the KY GPD stated that they considered making COVID-19 vaccination mandatory to program entry. Like ND HPACT2, the IA GPD respondent believed that mandating the vaccine for Veterans would create a barrier to accessing homeless services:“I actually had two staff members come talk to me separately and asked if I… was going to make the COVID-19 vaccine mandatory for all staff. And I had told them like I’m still doing my research, that hasn’t been determined yet. And both had said if it happened, I’ll be giving my resignation. And that they will not be getting the vaccine... It definitely caught me off guard.” (IA GPD)GPD providers in NJ and IA mentioned that COVID-19 vaccine hesitancy was a major challenge among their staff. The NJ participant said that 100% of their unvaccinated staff are African American and had expressed that they don’t trust the vaccine. The respondent worried that staff who decline vaccination may not be effective advocates to encourage Veteran vaccination. The IA respondent noted that two staff members would quit their jobs if the organization made COVID-19 vaccination mandatory for employment:The N.CA and MA respondents both reported initial apprehension about getting vaccinated but, upon learning more about the vaccine, ultimately overcame their hesitancy to protect their families.Accessibility, educational information, and trust were the primary factors that both HPACT providers and GPD staff identified as influential in increasing Veterans’ uptake of the COVID-19 vaccines. See Table The ND HPACT was able to get a high proportion of their Veterans vaccinated by holding two “blitzes”- special vaccination days at the HPACT clinic where they provided free food and giveaways and health professionals were available to answer Veterans’ questions about the vaccine. The HPACT clinic is more convenient and less intimidating than the VAMC, they said, so Veterans likely felt more comfortable getting vaccinated there. Further, ND respondents believed that seeing their peers getting vaccinated may have encouraged Veterans to get the vaccine.The GPD organizations in FL and MA facilitated uptake by having a VA and pharmacy team, respectively, come to their sites to administer the vaccine, making it easier and reducing both physical and perceived barriers for Veterans. In MA, having a team from the local pharmacy also improved access as even Veterans not eligible for VA healthcare could get the vaccine. Additionally, N.CA, NJ, and MA GPD respondents mentioned that the VA called both GPD staff and Veterans to let them know when the COVID-19 vaccine was available and helped them make appointments. All seven GPD sites provided transportation for Veterans to the VAMC if they wanted to get the COVID-19 vaccine.It would be a lot easier if… the VA could sort of set up shop and take care of the Veterans’ vaccines right then and there. Rather than one guy goes here, one guy goes there. If that could… ever be arranged… or even for the future even with flu shots, that would be extremely beneficial. A lot of our guys are older. And they still have that [hesitation toward] going to the doctor for anything at all. And so just to see the people actually coming to them and offering them assistance, I think would build a stronger trust between the guys and the VA healthcare.” (KY GPD)“HPACT and GPD providers agreed that lowering systemic barriers to accessing vaccines could improve uptake among Veterans experiencing homelessness, who already navigate a plethora of daily challenges. GPD staff in NJ and KY suggested that if the VA could vaccinate Veterans at their organization, it would reduce barriers, improve Veterans’ trust in the vaccine and the VA, and increase uptake:“Myself and other members of our leadership team have really been focused on having conversations with our staff about kind of coaching through how to… talk openly with your clients… and maintain that rapport that takes so long to build with the population that we serve, while also not giving them misinformation or persuading them in any way.” (IA GPD)Both HPACT and GPD providers mentioned providing educational information on COVID-19 vaccines to encourage Veterans to get vaccinated. GPD organizations in MA, FL, and NJ provided information to their clients or encouraged vaccination during regular meetings, N.CA distributed educational flyers to GPD residences, and IA was creating a Q&A panel with healthcare professionals. However, the MA, IA, and FL respondents also noted that they did not want to push their own opinions onto their clients:Conversely, the KY and S.CA GPD sites were not actively providing information as they were not seeing a lot of vaccine refusal among their clients. The S.CA respondent also noted that they were not providing educational information to Veterans because they did not believe they had the medical expertise to give advice on vaccination. Instead, Veterans were encouraged to contact their VA healthcare providers if they wanted a COVID-19 vaccine.“My population…becomes very defensive. …to the point where it’s like ‘let’s just stop it, I don’t want to go there’…. I try to make it very clear that this is a topic, once they say no and once they’ve voiced their concern… for them that’s the end of it, I don’t pursue any further because what I see is that after that… their mood changes and then they’re not able to focus on their appointment and what their medical condition is… when I see…their demeanor changes then I don’t pursue too much then” (CA HPACT3)HPACT staff at both sites encouraged vaccination. ND and CA nurses systematically identified Veterans to target for educational outreach. Veterans were called ahead of their scheduled medical appointments to inquire about vaccination status, and if unvaccinated, were encouraged to also schedule a vaccine appointment. If Veterans had questions, they offered to answer them over the phone or have them talk to their primary care provider. HPACT providers in CA similarly noted that it was important not to push hesitant Veterans for fear that they may stop coming to clinic altogether:One CA respondent cited that the VA had provided optional trainings to teach providers how to talk about the vaccine with Veterans and mentioned that he instructed his care team on how to do “motivational interviewing” to encourage patients to get vaccinated.“In [neighborhood], there’s this hashtag ‘can we live’. And it’s specifically aimed towards African Americans and other minorities to get vaccines and…[organizations] are putting up flyers and stuff in the community with facts and with images with people that look like them who have gotten vaccines…. [vaccine uptake] slowly started to increase. …And they also do…. these little blue packets that [GPD parent organization] drops off to our houses and the office… that they provide all of our clients that gives them updates, more facts, testimonials…” (N.CA GPD)Nearly all respondents agreed that Veterans need more education about the efficacy and safety of the COVID-19 vaccines. The FL GPD respondent suggested that information about how the vaccines work needs to be presented in simple visuals. N.CA GPD staff stated that messaging needs to be more targeted and culturally competent:“The HPACT team, the nurses and the provider, but also… case managers… have a huge role in discussing this with their Veterans, easing any concerns and worries they may have, not mandating it, not saying you have to get this, but encouraging them, explaining how it would be helpful, and certainly in some instances know that they could utilize more services if they had been vaccinated.” (ND HPACT2)GPD and HPACT staff at multiple sites noted that having trusted relationships with professionals sharing information with them about the vaccine was instrumental to Veterans’ vaccination decisions. The ND HPACT team continued providing face-to-face care throughout the pandemic, which they believed built trust with their Veterans. The respondents also noted that both the HPACT providers and housing program case managers discussed the COVID-19 vaccines with Veterans to ease their concerns:I have a rapport with some of the Veterans here, and other staff with others. And we talk to them… at our monthly house meeting, the superintendent said, ‘you know myself and [interviewee], we’re vaccinated, we’re fine. It’s something you should really consider doing’.” (NJ GPD)“A CA HPACT nurse cited that primary care providers were often better able to convince Veterans to get vaccinated than nurses because of their long history with patients, and another provider noted the importance of establishing relationships with their homeless patient population. Meanwhile, GPD staff in N.CA, NJ, and MA leveraged their close, personal relationships with Veterans to listen to their concerns and persuade them to accept the vaccine:“I always think that the Veteran community is totally different from the regular community…I know that the military background is a very strong bond…a lot of Veterans rely on other Veterans for [advice]….so they know what they’re getting themselves into. So, I think that if a lot of Veterans have a good positive outcome with the whole vaccine, you’re going to see a lot more Veterans get it that hesitated before because they see their fellow Veterans getting the vaccine and having positive results” (MA GPD)Both GPD & HPACT providers noted that Veterans tend to look to their peers in making health decisions, and recommended that the VA use Veterans as messengers to encourage vaccination and overcome hesitancy:People experiencing homelessness are particularly susceptible to severe COVID-19 disease due to underlying health conditions and are at an increased risk of exposure due to their congregate living environments , 6, 20. Early eligibility was important for increasing COVID-19 vaccination among people experiencing homelessness. The two GPD sites with the lowest vaccination rates (KY and IA) were in states that did not prioritize homeless shelters in their Phase 1 distribution plans . GPD resMisinformation about the safety, efficacy, and ingredients of the COVID-19 vaccines has led to widespread reluctance among both homeless and general populations , 10. NeaThis study reinforces previous research that found high levels of cynicism toward government entities among Veterans, which in turn has led to a distrust in the COVID-19 vaccines , 17, 34.Finally, Veterans have been shown to have differential health behaviors in some instances compared with the general population, likely due to past military experience, a complex relationship with the government, and military culture , 42–45. Limitations. Because of varying data collection methods, it may not be possible to accurately compare similarities and differences between HPACT and GPD sites, nor was it the intention of this study. Since sites were nonrandomly selected and included only seven states, findings are not generalizable to all clinics and organizations serving homeless Veterans in the U.S. However, care was taken to select sites representing a diverse range of geographic areas and patient/client sizes. Lastly, GPD respondents were interviewed when the Pfizer-BioNTech vaccine was only being administered under an Emergency Use Authorization (prior to its full authorization) by the U.S. Food and Drug Administration, and before the vaccines were widely available to the public, so we were not able to assess whether these events changed processes or uptake over time. Follow-up research is recommended. Future research should also explore the possible effects of the local political environment, which was outside the scope of this study and may affect state policies dictating vaccine prioritization, vaccination and other protective mandates, or funding for resources, all of which may influence vaccination uptake.Understanding the challenges and facilitators to getting Veterans experiencing homelessness vaccinated for COVID-19 will enable the VA, healthcare professionals, and homeless service providers to develop more effective policies and educational campaigns to increase uptake among this vulnerable population. Recommendations include providing convenient access to vaccines, using trusted sources, such as homeless program staff or Veteran peers, to provide educational information about the safety and efficacy of COVID-19 vaccines, and encouraging, rather than mandating, vaccination. Lessons learned could aid entities who deliver care to people experiencing homelessness with increasing vaccine uptake for COVID-19 booster shots, seasonal influenza, and other vaccines for transmissible diseases beyond the current pandemic.