This phase III clinical trial compared the immunogenicity and safety of a purified chick-embryo cell rabies vaccine (PCECV) administered according to a shortened post-exposure prophylaxis (PEP) 4-site/1-week intradermal regimen, compared with the currently recommended 2-site/Thai Red Cross (TRC) regimen. This controlled, open-label, multi-center study (NCT02177032) enrolled healthy individuals ≥1 year of age, randomized into 4 groups to receive intradermal PCECV according to one of the 2 regimens, with or without human rabies immunoglobulin (HRIG) administration at first visit (in adults only). Rabies virus neutralizing antibody (RVNA) concentrations and percentages of participants with RVNA concentrations ≥0. 5 IU/mL (considered as adequate concentrations following PEP) were assessed up to day (D) 365 post-first vaccination. Non-inferiority of the 4-site/1-week regimen to the 2-site/TRC regimen was demonstrated if at D49, the lower limit of the 95% confidence interval (CI) for the difference between groups in the percentage of participants with adequate RVNA concentrations was >-5%. Of the 443 participants receiving the 4-site/1-week regimen, 88 adults received HRIG; 442 participants received the 2-site/TRC regimen (88 with HRIG). All participants achieved adequate RVNA concentrations by D14. At D49, the difference in percentage of participants with adequate RVNA concentrations between the 4-site/1-week and the 2-site/TRC groups was -1 (95%CI: -2. 4–0. 0); thus, non-inferiority was concluded. RVNA geometric mean concentrations were 18 IU/mL in 4-site/1-week groups and 12 IU/mL in 2-site/TRC groups at D14, and subsequently declined in all groups. RVNA concentrations were consistently lower in adults with HRIG administration than in those without. The 2 regimens had similar safety profiles. Of the 15 serious adverse events reported in 4-site/1-week groups and 19 in 2-site/TRC groups, none were vaccination-related. The data suggest that the 4-site/1-week regimen might be an alternative to current recommendations, with potential benefits in terms of improved cost-efficiency and compliance to vaccination.
Rabies is an acute viral disease, caused by viruses belonging to the Lyssavirus genus of the Rhabdoviridae family [1]. Although rabies is almost eliminated in industrialized countries, it is still estimated to cause more than 60,000 deaths each year worldwide, of which the vast majority occur in Asia and Africa [2]. Despite the fact that the disease is completely preventable and that recent massive campaigns targeting its elimination were launched in endemic regions [3], rabies continues to be listed as a neglected tropical disease by the World Health Organization (WHO) [4]. Prevention of rabies by post-exposure prophylaxis (PEP), including vaccination, is highly effective when administered promptly after suspected exposure. Current recommendations also indicate concomitant administration of rabies immunoglobulins (RIG) for WHO category III rabies exposures [5]. In endemic regions, intradermal (ID) vaccination regimens have proven to be more cost-effective than intramuscular (IM) ones and are therefore used preferentially. The recommended WHO ID regimen for PEP, the updated 2-site Thai Red Cross (2-site/TRC) regimen, takes approximately 1 month and requires 4 clinic visits with 2 doses of vaccine administered on each of the days (D) 0,3, 7, and 28 [1]. However, to date, prevention of rabies remains inadequate in developing regions, where access to medical care is not optimal [6]. Reducing the number of required visits would reduce costs, while at the same time increasing compliance to the full PEP course. A newly proposed PEP regimen (not yet recommended by the WHO) allows completion of the ID immunization within 1 week through administration of 4 vaccine doses on D0, D3, and D7, and has shown encouraging results in clinical trials (4-site/1week) [7,8]. This study aimed to demonstrate the non-inferiority of the immune response following vaccination with a purified chick embryo cell culture vaccine (PCECV) according to the new 4-site/1-week ID regimen compared to the updated conventional 2-site/TRC ID regimen with or without concomitant administration of human RIG (HRIG).
This was a phase III, randomized, age-stratified, controlled, open-label study carried out in 4 centers in the Philippines and 2 centers in Thailand, between June 2014 and August 2015. The study enrolled healthy individuals ≥1 year of age, who had never received rabies vaccines or RIG, had not previously been exposed to rabies, and had no history of allergy or contraindications to the study vaccine or HRIG components. Pregnant women were not enrolled in the study. The full list of exclusion criteria is presented in S1 Text. Individuals were enrolled based on the following age strata: 1–5 years, 6–17 years, and ≥18 years. Children and adolescents younger than 18 years were randomly assigned (1: 1) to one of the groups receiving PCECV according to the 4-site/1-week ID regimen (Group A1) or the 2-site/TRC regimen (Group B1). Adults were randomized (2: 1: 2: 1) into 4 groups to receive PCECV according to the 4-site/1-week ID regimen alone (Group A1) or with concomitant HRIG administration at first visit (Group A2), or PCECV according to the 2-site/TRC ID regimen alone (Group B1) or with concomitant HRIG administration at first visit (Group B2) (Fig 1; S2 Text). The participants or their parents/legally accepted representatives (LARs) were required to be able to understand and comply with all study procedures, and a written informed consent was obtained before study enrolment. The study was conducted in accordance with the Declaration of Helsinki and the principles of Good Clinical Practice. The study protocol, amendments, and informed consent forms from the participants or their parents/LARs were reviewed and approved by regional Independent Ethics Committees. The study is registered at ClinicalTrials. gov (NCT02177032). All patient-level data were anonymized. The primary objective was to assess non-inferiority of the immune response of the 4-site/1-week ID PEP regimen to that of the currently recommended 2-site/TRC ID regimen of PCECV, with or without HRIG administration, as measured by the percentage of participants with rabies virus neutralizing antibody (RVNA) concentrations ≥0. 5 international units (IU) /mL in the whole study population, at D49. Non-inferiority was demonstrated if the lower limit (LL) of the 2-sided 95% confidence interval (CI) around the difference (Group A1 + Group A2 minus Group B1 + Group B2) in the percentage of participants with RVNA concentrations ≥0. 5 IU/mL was greater than -5%. Non-inferiority of the immune response of the 4-site/1-week ID PEP regimen to that of the currently recommended 2-site/TRC regimen of PCECV, with or without HRIG administration, was also tested in terms of RVNA geometric mean concentrations (GMCs) in the whole study population, at D49. Non-inferiority was demonstrated if the LL of the 2-sided 95% CI around the GMC ratio (Group A1 + Group A2 over Group B1 + Group B2) was >0. 667. Considering the average incubation period for rabies (between 20 and 60 days) [9] and to allow the immunogenicity evaluation at approximately 3 weeks after last vaccine administration (D28 for Groups B1 and B2), D49 was selected as time point for the assessment of the non-inferiority endpoints. Other secondary objectives compared the antibody responses at D7, D14, D90, D180, and D365, in terms of RVNA GMCs and percentages of participants with RVNA concentrations ≥0. 5 IU/mL following each PCECV regimen, in the entire study population and in adults only, and in study groups with and without HRIG administration. The safety and tolerability of both PCECV regimens were also evaluated. PCECV is a lyophilized vaccine produced from the Flury LEP-25 strain grown in primary cultures of chick fibroblasts and inactivated with β-propiolactone [10,11]. Prior to administration, PCECV (commercial lot 2470, with a potency of 6. 87 IU/mL) was reconstituted with sterile water for injection to yield a final volume of 1 mL. At each vaccination visit (Fig 2), participants in Groups A1 and A2 received 4 injections of 0. 1 mL of PCECV (one dose in each deltoid and anterolateral thigh area), while participants in Groups B1 and B2 received 2 injections of 0. 1 mL of PCECV (one dose in each deltoid). All injections were administered via ID route. A dose of 20 IU/kg body weight of commercially available HRIG (Berirab, Behring GmbH, lot number 08547142) was administered on D0, concomitantly with the vaccination, to all adults in Groups A2 and B2, by IM injection into the gluteal muscle. Because this was a simulated PEP study in healthy volunteers, the use of HRIGs was preferred to those of equine origin, in order to avoid exposing study participants to any potential (although usually rare) safety issues, linked to the use of material of heterologous origin. Blood samples (approximately 5 mL) for immunogenicity testing were collected at D0,7, 14,49,90,180, and 365 (Fig 2). RVNA levels were assessed by the rapid fluorescent focus inhibition test [12], which was performed at the Kansas State University Rabies Laboratory, Manhattan, KS, United States [13]. RVNA concentrations ≥0. 5 IU/mL by D14 are considered by the WHO as an adequate response to rabies PEP [1]. After each vaccination, all participants were observed for at least 30 minutes and evaluated for adverse events (AEs). Participants or their parents/LARs recorded any AEs occurring after this interval on diary cards, which they returned at the next visit. All solicited local and systemic AEs were recorded for 3 days (D0–2) following first vaccination visit, 4 days following second vaccination visit, and 7 days following third and fourth (for Groups B1 and B2 only) vaccination visits. Solicited local AEs were induration, swelling, erythema, and tenderness for children 1–5 years of age, and induration, swelling, erythema, and pain for participants older than 6 years. Solicited systemic AEs were change in eating habits, sleepiness, vomiting, diarrhea, and irritability in the 1–5 years age stratum, and generalized arthralgia, headache, fatigue, rash, vomiting, diarrhea, and loss of appetite in all other participants. Solicited AEs that were not resolved during the post-vaccination observation periods were also recorded as unsolicited AEs. The relationship between AEs and study treatment (“not related”, “possibly related”, and “probably related”) was determined by the investigators. Unsolicited AEs were followed for 29 and 50 days after each vaccination for participants in Groups A1 and A2 and Groups B1 and B2, respectively. Serious AEs (SAEs) and AEs leading to withdrawal were recorded throughout the study. A SAE was defined as any untoward medical occurrence that resulted in death, hospitalization or prolongation of hospitalization, persistent or significant disability/incapacity, congenital anomaly or birth defect, or was life-threatening. Immunogenicity assessments were carried out in the per-protocol sets (PPSs) at each time point, including all participants who complied with the vaccination schedule, had immunogenicity data at the relevant time points, and did not have major protocol deviations. The non-inferiority objectives were assessed in the primary PPS (PPS at D49). The percentage of participants with RVNA concentrations ≥0. 5 IU/mL and RVNA GMCs were tabulated with 95% CIs for each group, by time point and age stratum. Between-group differences in the percentage of participants with RVNA concentrations ≥0. 5 IU/mL were calculated using a binomial distribution, and associated CIs were constructed using the Miettinen-Nurminen method [14]. The GMCs, the within-group geometric mean ratios, and the associated 2-sided 95% CIs for each group were computed by the exponentiation of the least square means of the logarithmically transformed concentrations (and their differences), and the 95% CIs were obtained from an analysis of variance with vaccine regimen, age stratum, and center as factors. Safety assessments were performed in the safety set, which included participants who had received at least one dose of PCECV and had solicited or unsolicited AE data (i. e. , any safety information) post-vaccination. The number and percentage of participants with solicited and unsolicited AEs, and SAEs were reported for each vaccine group and for each age stratum. Analyses were performed using SAS (Statistical Analysis System) 9. 1 software. For the primary objective, the high lethality of rabies was taken into account to establish the non-inferiority margin. Based on previous studies, where the vast majority of participants achieved adequate RVNA concentrations after 4 PCECV doses [15], the percentages of participants with RVNA concentrations ≥0. 5 IU/mL were assumed to reach 97% in Groups A1 and B1,95% in Groups A2 and B2, and 96% in the whole population. Accounting for a non-evaluable/drop-out rate of 20%, non-inferiority could be shown with a power of 89. 8% for a total of 876 enrolled participants (438 in Groups A1 and A2 and 438 in Groups B1 and B2). Sample size and power estimations were computed using the Query Advisor 7. 0 software.
Out of the 885 enrolled participants, all attended at least 1 visit, and 875 completed the study. Disposition of participants by groups, reasons for withdrawal from the study, and protocol deviations leading to elimination from the primary PPS are given in Fig 1. The mean age was 22. 9 years, 54% of participants were female and all were of Asian heritage. Study groups were balanced in terms of demographic and baseline characteristics, apart from age (due to the assignment of only adults in groups receiving HRIG) (Table 1). Compliance with the vaccination schedule was high, with at least 98% of participants in Groups A1, A2 and B1 and all participants in Group B2 receiving all vaccine doses as planned. At D49, the percentages of participants with RVNA concentrations ≥0. 5 IU/mL were 99% (95% CI: 98%–100%) in groups receiving the 4-site/1-week ID regimen (Group A1 + Group A2), and 100% (95% CI: 99%–100%) in groups receiving the 2-site/TRC ID regimen (Group B1 + Group B2). The LL of the 2-sided 95% CI on the between-group difference was -2. 4% which is above the pre-specified non-inferiority margin. Thus, the primary objective was met. In the whole population, for both vaccination regimens, all participants achieved RVNA concentrations ≥0. 5 IU/mL by D14 and the vast majority of them (90% in Group A1 + Group A2 and 83% in Group B1 + Group B2), maintained adequate RVNA concentrations at 1 year (D365) after first vaccination (Table 2). RVNA GMCs peaked at D14 and declined at subsequent time points. At D49, the RVNA GMC ratio (Group A1 + Group A2 over Group B1 + Group B2) was 0. 46 (95% CI: 0. 37–0. 58), and the LL of the 95% CI was below the pre-specified non-inferiority margin; thus, the secondary objective was not met. At D365, a higher immune response was observed in the groups receiving the 4-site/1-week regimen than in those receiving the 2-site/TRC regimen, as shown by the between-group GMC ratios (Table 2). In groups not receiving HRIG, all study participants achieved adequate RVNA levels by D14, and a higher proportion of participants in Group A1 (95%) than in Group B1 (87%) maintained adequate neutralizing antibody levels for 1 year following first vaccination (Table 2). In both groups, RVNA GMCs peaked at D14 and then declined up to D365, with higher values being observed in Group A1 than in Group B1 at D14 and D365 (Table 2). At all-time points except D14, the percentage of adults with adequate RVNA concentrations was lower in Group A2 than in group A1 (Table 2). RVNA GMCs were consistently lower in Group A2 than in Group A1 (Table 2). Comparable percentages of adults with RVNA concentrations ≥0. 5 IU/mL were observed for groups A2 and B2 for all time points, except at D90 when the percentage of adults with adequate RVNA levels was significantly lower in Group A2 than in Group B2 (Table 2). RVNA GMCs peaked in both groups at D14, when a significantly higher GMC was observed in Group A2 than in Group B2. RVNA levels declined in both groups at subsequent time points (Table 2). The same trend as described for the overall population was observed in the different age strata evaluated, including in the youngest participants (children 1–5 years of age). At least 1 solicited AE was reported in 57% (Group A1) and 65% (Group A2) of participants receiving the 4-site/1 week regimen and in 59% (Group B1) and 62% (Group B2) of participants receiving the 2-site/TRC regimen (Table 3). Solicited local reactions were more frequent in the 1–5 years age stratum (76% and 68% of children in Groups A1 and B1, respectively) than in the other age strata (31%–41% and 33%–41% of individuals receiving the 4-site/1-week ID regimen and the 2-site/TRC ID regimen, respectively; S1 Table). The most frequently reported solicited local AEs were injection site tenderness in the 1–5 years age stratum (ranging from 7% to 21% of children across study groups), injection site pain in the 6–17 years age stratum (in 4–14% of participants in all groups), and injection site erythema in the ≥18 years age stratum (ranging from 1% to 16% of adults across study groups). Solicited systemic AEs were reported in 33%–42% of participants receiving the 4-site/1-week ID regimen and 33%–46% of participants receiving the 2-site/TRC ID regimen (Table 3) and were more frequently reported in the ≥18 years age stratum (S1 Table). After any vaccination, the most frequent solicited systemic AEs were fever (reported in 7% of children in Group A1 and 17% in Group B1) and sleepiness (in 14% and 13% of children in Groups A1 and B1, respectively) in the 1–5 years age stratum; and headache (in 13% of participants in Group A1 and 16% in Group B1) and fatigue (for 12% of participants in Group A1 and 11% in Group B1) in the 6–17 years age stratum. After any vaccination, headache (with incidences ranging from 19% in Group B1 to 35% in Group B2) and fatigue (ranging from 19% in Group A2 to 27% in Group B2) were also the most frequently reported solicited systemic AEs for participants aged ≥18. Severe solicited local and systemic AEs were reported in 0%–2% of participants in all age groups; most solicited AEs were mild to moderate in intensity. Unsolicited AEs were reported in 73% and 84% of participants in Groups A1 and A2, respectively, and in 79% and 82% of participants in Groups B1 and B2, respectively. Unsolicited AEs at least possibly or probably related to vaccination were reported in 66%, 84%, 65%, and 80% of participants in Groups A1, A2, B1, and B2, respectively (Table 3). The incidence of severe unsolicited AEs at least possibly or probably related to vaccination was 1% in Groups A1 and B1 and 0% in Groups A2 and B2. The most frequently reported AEs after any vaccination were in the “general disorders and administration site conditions” system organ class, followed by “infections and infestations”. Overall, the most frequent AE was injection site erythema, with incidences ranging from 37% (Group B1) to 61% (Group A2) of participants in all groups. No AEs leading to withdrawal from the study were reported. SAEs were reported in 3%–6% of participants; none of them were considered related to vaccination (Table 3). All SAEs except 1 (HIV infection in an adult in Group A1) were recovered/resolved by the end of the study. No deaths were reported during the study.
The administration of PCECV according to a 4-site/1-week ID regimen for rabies PEP was non-inferior to that according to a 2-site/TRC ID regimen in terms of percentages of participants with RVNA concentrations ≥0. 5 IU/mL at D49. The elicited immune responses peaked at D14, and subsequently declined up to D365. RVNA concentrations were consistently lower in individuals with concomitant HRIG administration compared to adults not receiving HRIG, confirming previous observations. However, this was not considered to be clinically relevant, as HRIG administration is part of the recommended PEP procedures. Overall, both PEP regimens were well tolerated. If included in national and supra-national recommendations for rabies PEP, the 4-site/1-week ID regimen might be a valid alternative to currently recommended 2-site/TRC ID PEP regimen.
Rabies is a deadly, but vaccine-preventable disease which still causes tens of thousands of deaths yearly, mostly in Asia and Africa. Rabies virus is spread via the saliva of infected mammals to humans, usually through bites or contamination of open wounds. Access to measures like wound cleansing with soap and rabies vaccination immediately after contact with a suspected rabid animal (exposure) can be life-saving. The post-exposure vaccination schedule currently recommended by the World Health Organization for intradermal injection is the Thai Red Cross regimen, requiring 4 clinic visits in one month, with 2 injections given at each visit on days (D) 0 (day of the contact), 3,7, and 28. In this study, we evaluated the antibody responses and the safety profile of a new shortened schedule, requiring 3 clinic visits and only 1 week to complete, consisting of 4 intradermal injections given at each visit on D0,3, and 7 (the 4-site/1-week regimen). The study was conducted in the Philippines and Thailand which enrolled 885 healthy volunteers, at least 1 year of age, with no real exposure to rabies. The two schedules induced adequate antibody responses in similar proportion of volunteers at day 49. The vaccine administration according to both schedules was well tolerated.
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Shortening intradermal rabies post-exposure prophylaxis regimens to 1 week: Results from a phase III clinical trial in children, adolescents and adults