Purified Vero Cell Rabies Vaccine (PVRV, Verorab®): A Systematic Review of Intradermal Use Between 1985 and 2019

The purified Vero cell rabies vaccine (PVRV; Verorab®, Sanofi Pasteur) has been used in rabies prevention since 1985. Evolving rabies vaccination trends, including shorter intradermal (ID) regimens with reduced volume, along with WHO recommendation for ID administration has driven recent ID PVRV regimen assessments. Thus, a consolidated review comparing immunogenicity of PVRV ID regimens during pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) is timely and beneficial in identifying gaps in current research. A search of seven databases for studies published from 1985 to November 2019 identified 35 studies. PrEP was assessed in 10 studies (n = 926) with 1-3-site, 1-3-visit regimens of up to 3-months duration. Seroconversion (rabies virus neutralizing antibodies [RVNA] ≥ 0.5 IU/mL) rates of 90-100% were reported within weeks, irrespective of regimen, with robust booster responses at 1 year (100% seroconversion rates by day 14 post-booster). However, data are lacking for the current WHO-recommended, 2-site, 1-week ID PrEP regimen. PEP was assessed in 25 studies (n = 2136) across regimens of 1-week to 90-day duration. All ID PEP regimens assessed induced ≥ 99% seroconversion rates (except in HIV participants) by day 14-28. This review confirms ID PVRV suitability for rabies prophylaxis and highlights the heterogeneity of use in the field.

Rabies Antibody Response After Booster Immunization: A Systematic Review and Meta-analysis

Although fatal once symptomatic, rabies is preventable by administration of pre- and post-exposure vaccines. International guidelines suggest lifelong protection by a pre-exposure vaccination scheme followed by timely post-exposure vaccines. Rapidity and magnitude of the antibody recall response after booster inoculation are essential, as many people have been previously immunized a long time ago. The objective of this study was therefore to systematically review the evidence on the boostability of rabies immunization to date. We included 36 studies, of which 19 studies were suitable for meta-analysis. Reduced antibody levels were found after intradermal primary schedules as compared to intramuscular schedules. However, responses after booster immunization were adequate for both routes. Although studies showed that antibody levels decline over time, adequate booster responses were still retained over long time intervals indicating that post-exposure treatment is effective without extra measures after long periods of time.

An overview of the immunogenicity and effectiveness of current human rabies vaccines administered by intradermal route

Pre- as well as post-exposure prophylaxis plays an important role in controlling the number of deaths associated with human rabies. Rabies vaccines, classically injected intramuscularly, are now also administered by intradermal (ID) route. Vaccines to be administered by the ID route should meet the same quality, safety and efficacy specifications as vaccines for intramuscular (IM) use. The aim of this paper is to provide information based on publicly available data regarding the ID use of rabies vaccines and to identify potential needs for further analysis of the potency, immunogenicity and effectiveness of rabies vaccines administered by this route. A first literature search, focused on the immunogenicity of rabies vaccines given by ID route, identified 338 publications in the period 1997-2018, 40 of which were included in our analyses. A second search investigating the effectiveness of ID vaccination resulted in 371 hits for the period 2007-2018, of which 13 suitable publications were retained. The immunogenicity of current rabies vaccines was analyzed in 3 ways: proportion of subjects reaching the antibody threshold of 0.5 IU/ml after ID vaccination, relationship between potency and immunogenicity of the vaccine given intradermally, and comparison of antibody responses after IM or ID vaccination. Overall, vaccines administered intradermally were found immunogenic. Post-exposure prophylaxis by ID route appeared at least as immunogenic as by IM regimens. By contrast, ID pre-exposure prophylaxis trended towards lower antibody titers than IM vaccination, but the observation was not associated with any clinical relevance. Vaccine effectiveness was assessed by investigating survival after exposure. Data from more than 30,000 patients who sought rabies post-exposure prophylaxis did not indicate that current vaccines administered by ID route lack efficacy. These results support current recommendations for ID vaccination against rabies. However, published data on ID performance were associated with significant weaknesses that future research should better address.

Immunogenicity and safety of WHO-approved TRC-ID regimen with a chromatographically purified Vero cell rabies vaccine with or without rabies immunoglobulin in children

INTRODUCTION

Children are at risk of rabies exposure in many Asian countries. The safety and immunogenicity profile of the WHO-approved two-site intradermal Thai Red Cross regimen (modified TRC-ID regimen; 2-2-2-0-2) with a new chromatographically purified Vero-cell rabies vaccine (CPRV) is lacking. Area covered: We studied the safety and immunogenicity of the TRC-ID regimen with a new CPRV in non-immunized Thai children with possible or proven rabies exposure. Thirty-nine seronegative patients (age range 2-14 years) with rabies exposure (WHO categories II or III) received two 0.1-mL intradermal doses of CPRV at both deltoid regions on days 0, 3, 7, and 28. Twenty-five patients (64.1%) received rabies immunoglobulin due to having rabies exposure, according to WHO category III. All serum samples were tested for rabies neutralizing antibody (Nab) by the rapid fluorescent focus inhibition test (RFFIT) before vaccination, and on days 14 and 90 after vaccination. All patients had an adequate immune response (Nab titers ≥ 0.5 IU/mL) on days 14 and 90. No patients died of rabies infection. No serious adverse reactions were observed. Expert commentary: CPRV is economic, safe, and immunogenic if given as the modified TRC-ID regimen in children.

A randomized non-inferiority clinical study to assess post-exposure prophylaxis by a new purified vero cell rabies vaccine (Rabivax-S) administered by intramuscular and intradermal routes

BACKGROUND

Rabies is a 100% fatal disease but preventable with vaccines and immunoglobulins. We have developed a new purified vero cell rabies vaccine (Rabivax-S) and evaluated its safety and immunogenicity in post-exposure prophylaxis by intramuscular (IM) and intradermal (ID) routes.

METHODS

This was a randomized active-controlled non-inferiority study in 180 individuals (age 5years and above) with suspected rabies exposure (90 each with WHO Category II and Category III exposures). The participants received either Rabivax-S (1mL IM; five doses), Rabivax-S (0.1mL ID; eight doses) or purified chick embryo cell vaccine (PCEC, Rabipur®) (1mL IM; five doses). The IM doses were given on Day 0, 3, 7, 14 and 28 while the ID doses were given on days 0, 3, 7 and 28. Category III patients also received a human rabies immunoglobulin (HRIG) on Day 0. Adverse events (AEs) were recorded with diary cards till day 42. Rabies neutralizing antibody levels were measured on day 0, 7, 14, 28 and 42.

RESULTS

In both the category II and III patients, the geometric mean concentration (GMC) ratios of Rabivax-S IM and Rabivax-S ID groups to PCEC IM were more than 1, thus proving the non-inferiority. GMCs were similar or higher in Rabivax-S groups at all the time points. Seroresponse against rabies (RFFIT titre⩾0.5IU/mL) was achieved in all participants. Mostly mild local and systemic adverse events were reported across the three groups and all resolved without sequelae.

CONCLUSIONS

Rabivax-S was well tolerated and showed immunogenicity comparable to a licensed rabies vaccine by both IM and ID routes in post-exposure prophylaxis. Registry No.: CTRI/2012/11/003135.