Potency requirements of rabies vaccines administered intradermally using the Thai Red Cross regimen: investigation of the immunogenicity of serially diluted purified chick embryo cell rabies vaccine

Challenges of Rabies Serology: Defining Context of Interpretation

The case fatality rate of rabies, nearly 100%, is one of the most unique characteristic of this ancient virus infection. The crucial role rabies virus neutralizing antibody plays in protection is both well established and explanation of why rabies serology is important. Various laboratory methods can and have been used but serum neutralization methods have long been the gold standard due to the ability to measure function (neutralization), however these methods can be difficult to perform for several reasons. Assays such as enzyme linked absorbance assays (ELISA), indirect fluorescence antibody (IFA) and more recently lateral flow methods are in use. Interpretation of results can be problematic, not only between methods but also due to modifications of the same method that can lead to misinterpretations. A common assumption in review of laboratory test results is that different methods for the same component produce comparable results under all conditions or circumstances. Assumptions and misinterpretations provide the potential for detrimental decisions, ranging from regulatory to clinically related, and most importantly what ‘level’ is protective. Review of the common challenges in performance and interpretation of rabies serology and specific examples illuminate critical issues to consider when reviewing and applying results of rabies serological testing.

Safety and immunogenicity of SURE RAB™, an inactivated cell culture derived rabies vaccine: A comparative, phase III clinical trial

INTRODUCTION

Rabies is a viral zoonotic disease widespread across the world. In India, various cell culture vaccines are available for pre and post exposure prophylaxis (PEP) but are not sufficient to meet the rising demand. The present study evaluated the safety and immunogenicity of Rabies vaccine Human I.P. (Brand name: SURE RAB™) in PEP and demonstrated its non-inferiority to already approved rabies vaccine (Brand name: VERORAB).

MATERIAL AND METHODS

It was a phase-III randomized, open label, comparative, single centre clinical trial in post exposure subjects. Safety and immunogenicity were evaluated at Day 0, 14 and 45 ± 7 post vaccination. Day 14 serum samples were analyzed by Enzyme Linked Immunesorbent assay (IgG ELISA, Bio-Rad) and Day 0, 14 and 45 ± 7 serum were tested by Rapid Fluorescent Focus Inhibition Test (RFFIT). Paired t-test was applied to compare the results of Rabies virus neutralizing antibody (RVNA). The severity of adverse reactions was measured on a scale of excellent, good, fair and bad; p-value (p < 0.05) was considered as statistically significant.

RESULTS

All the subjects achieved a protective titer value between 0.5 and 9.0 IU/ml by Day 14 tested by ELISA and significant rise in the antibody titer in all the groups when tested after 45 days. Statistically significant p-value (p < 0.001) observed with RFFIT test indicated biological potency of rabies vaccine. Adverse events and safety was comparable statistically between three groups (p ​= ​0.886) and Group I ​+ ​II combined versus Group III (p = 0.495).

CONCLUSION

The study results conclusively demonstrate that SURE RAB™ is comparable to VERORAB in terms of safety and immunogenicity and can be used for PEP in rabies.

Rabies post-exposure vaccination in 2 visits within a week: A 4-site intradermal regimen

Rabies is fatal in all unvaccinated patients bitten by dogs, and so post-exposure vaccine regimens must be robust enough to ensure their survival under all conditions. Treatment tends to be excessive for most people, but there is justified anxiety about reducing vaccine dosage and shortening regimens. Recently, World Health Organisation (WHO) recommended one week primary post-exposure intradermal regimens requiring 3 clinic visits, but these are unlikely to prove economical where rabies vaccination is most needed, in deprived rural areas of Africa and Asia. A highly immunogenic regimen involving two doses of intradermal vaccine given one week apart has advantages over other regimens. Anyone exposed to a possibly rabid animal would be given intradermal (ID) injections at 4 sites using a whole vial of vaccine. Those who had not been previously vaccinated would be given 2-site ID injections using half a vial one week later. Those who might be immunosuppressed could be given an optional single ID dose on day 28. The rationale for this regimen is discussed in the context of the recently revised WHO recommendations for rabies prophylaxis.

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.

Post-exposure prophylaxis (PEP) for rabies with purified chick embryo cell vaccine: a systematic literature review and meta-analysis

INTRODUCTION

Fifteen million people each year receive post-exposure prophylaxis (PEP) to prevent rabies, yet the disease remains neglected and highly under-reported.

AREAS COVERED

In this systematic literature review, we assessed the immunogenicity, efficacy, and safety of a purified chick embryo cell-culture rabies vaccine (PCECV) for PEP against rabies by intramuscular (IM) or intradermal (ID) administration. We performed meta-analyses to compare immunogenicity according to the route of vaccine administration, study population, and PEP regimen, such as number of doses, and concomitant rabies immunoglobulin.

EXPERT COMMENTARY

There were 54 estimates of immune responses to vaccination, which showed that in the overall population, after starting PEP with PCECV by the IM or ID route (≥2.5 IU per dose), almost all individuals had rabies virus neutralizing antibody (RVNA) titers above the World Health Organization (WHO) recommended serological threshold for an adequate immune response to vaccination (RVNA ≥0.5 IU/ml by day 14). In the overall population, PCECV had an acceptable safety profile. However, given that there are 59,000 human rabies deaths reported annually, the challenge is to improve access to PCECV for PEP against human rabies.

Single visit rabies pre-exposure priming induces a robust anamnestic antibody response after simulated post-exposure vaccination: results of a dose-finding study

BACKGROUND

The current standard 3-dose intramuscular rabies PrEP schedule suffers from a number of disadvantages that severely limit accessibility and availability. The cost of is often prohibitive, it requires 3 visits to the clinic, and there are regular vaccine shortages.

METHODS

Volunteers ( N  = 30) were randomly assigned to 4 study arms: 1 standard dose intramuscular (IM) dose of PVRV (purified Vero cell rabies vaccine, Verorab), and 1/5th, 2/5th or 3/5th- fractional intradermal (ID) dose of PVRV in a single visit. All subjects received a simulated rabies post-exposure prophylaxis (D0, D3) 1 year later. Rabies virus neutralizing antibodies (RVNA) were determined by virus neutralization microtest (FAVN) on D0, D7, D28, Y1 and Y1 + D7.

RESULTS

28 out of 30 subjects (93%) seroconverted 1 month after primary vaccination; 1 subject in the 1-dose IM arm and 1 in the 1/5th-fractional dose ID arm did not. After 1 year, 22 out of 30 subjects (73%) no longer had RVNA above 0.5 IU/ml, with no discernible difference between study groups. After 1 year, all 30 subjects mounted a booster response within 7 days after simulated PEP, with the highest titers found in the single dose IM group ( P  < 0.03).

CONCLUSIONS

This dose finding study demonstrates that priming with a single dose of rabies vaccine was sufficient to induce an adequate anamnestic antibody response to rabies PEP in all subjects 1 year later, even in those in whom the RVNA threshold of 0.5 IU/ml was not reached after priming.

Risk factors for inadequate antibody response to primary rabies vaccination in dogs under one year of age

Ensuring the adequacy of response to rabies vaccination in dogs is important, particularly in the context of pet travel. Few studies have examined the factors associated with dogs' failure to achieve an adequate antibody titer after vaccination (0.5 IU/ml). This study evaluated rabies antibody titers in dogs after primary vaccination. Dogs under one year of age whose serum was submitted to a reference laboratory for routine diagnostics, and which had no prior documented history of vaccination were enrolled (n = 8,011). Geometric mean titers (GMT) were calculated and univariate analysis was performed to assess factors associated with failure to achieve 0.5 IU/mL. Dogs vaccinated at >16 weeks of age had a significantly higher GMT compared to dogs vaccinated at a younger age (1.64 IU/ml, 1.57-1.72, ANOVA p < 0.01). There was no statistical difference in GMT between dogs vaccinated <12 weeks and dogs vaccinated 12-16 weeks (1.22 IU/ml and 1.21 IU/ml). The majority of dogs failed to reach an adequate titer within the first 3 days of primary vaccination; failure rates were also high if the interval from vaccination to titer check was greater than 90 days. Over 90% of dogs that failed primary vaccination were able to achieve adequate titers after booster vaccination. The ideal timing for blood draw is 8-30 days after primary vaccination. In the event of a failure, most dogs will achieve an adequate serologic response upon a repeat titer (in the absence of booster vaccination). Booster vaccination after failure provided the highest probability of an acceptable titer.

A single center, open label study of intradermal administration of an inactivated purified chick embryo cell culture rabies virus vaccine in adults

In the USA, rabies vaccines (RVs) are licensed for intramuscular (IM) use only, although RVs are licensed for use by the intradermal (ID) route in many other countries. Recent limitations in supplies of RV in the USA reopened discussions on the more efficient use of available biologics, including utilization of more stringent risk assessments, and potential ID RV administration. A clinical trial was designed to compare the immunogenic and adverse effects of a purified chicken embryo cell (PCEC) RV administered ID or IM. Enrollment was designed in four arms, ID Pre-Exposure Prophylaxis (Pre-EP), IM Pre-EP, ID Booster, and IM Booster vaccination. Enrollment included 130 adult volunteers. The arms with IM administration received vaccine according to the current ACIP recommendations: Pre-EP, three 1mL (2.5 I.U.) RV doses, each on day 0, 7, and 21; or a routine Booster, one 1ml dose. The ID groups received the same schedule, but doses administered were in a volume of 0.1mL (0.25 I.U.). The rate of increase in rabies virus neutralizing antibody titers 14-21days after vaccination were similar in the ID and correspondent IM groups. The GMT values for ID vaccination were slightly lower than those for IM vaccination, for both naïve and booster groups, and these differences were statistically significant by t-test. Fourteen days after completing vaccination, all individuals developed RV neutralizing antibody titers over the minimum arbitrary value obtained with the rapid fluorescent focus inhibition test (RFFIT). Antibodies were over the set threshold until the end of the trial, 160days after completed vaccination. No serious adverse reactions were reported. Most frequent adverse reactions were erythema, induration and tenderness, localized at the site of injection. Multi use of 1mL rabies vaccine vials for ID doses of 0.1 was demonstrated to be both safe and inmunogenic.

Reducing Cost of Rabies Post Exposure Prophylaxis: Experience of a Tertiary Care Hospital in Pakistan

BACKGROUND

Rabies is a uniformly fatal disease, but preventable by timely and correct use of post exposure prophylaxis (PEP). Unfortunately, many health care facilities in Pakistan do not carry modern life-saving vaccines and rabies immunoglobulin (RIG), assuming them to be prohibitively expensive and unsafe. Consequently, Emergency Department (ED) health care professionals remain untrained in its application and refer patients out to other hospitals. The conventional Essen regimen requires five vials of cell culture vaccine (CCV) per patient, whereas Thai Red Cross intradermal (TRC-id) regimen requires only one vial per patient, and gives equal seroconversion as compared with Essen regimen.

METHODOLOGY/PRINCIPAL FINDINGS

This study documents the cost savings in using the Thai Red Cross intradermal regimen with cell culture vaccine instead of the customary 5-dose Essen intramuscular regimen for eligible bite victims. All patients presenting to the Indus Hospital ED between July 2013 to June 2014 with animal bites received WHO recommended PEP. WHO Category 2 bites received intradermal vaccine alone, while Category 3 victims received vaccine plus wound infiltration with Equine RIG. Patients were counseled, and subsequent doses of the vaccine administered on days 3, 7 and 28. Throughput of cases, consumption utilization of vaccine and ERIG and the cost per patient were recorded.

CONCLUSIONS/SIGNIFICANCE

Government hospitals in Pakistan are generally underfinanced and cannot afford treatment of the enormous burden of dog bite victims. Hence, patients are either not treated at all, or asked to purchase their own vaccine, which most cannot afford, resulting in neglect and high incidence of rabies deaths. TRC-id regimen reduced the cost of vaccine to 1/5th of Essen regimen and is strongly recommended for institutions with large throughput. Training ED staff would save lives through a safe, effective and affordable technique.

Evaluation of a new five-injection, two-site,intradermal schedule for purified chick embryo cell rabies vaccine: A randomized, open-label, active-controlled trial in healthy adult volunteers in India

BACKGROUND

Human rabies is an ongoing significant public health problem inmany developing countries, with India reporting the highest incidence of rabies-related deaths (∼20,000 per year). Many people living in India cannot afford the standard IM postexposure prophylaxis (PEP) with cell-culture vaccines, which are administered using a 5-dose regimen developed in Essen, Germany. A potentially less expensive intradermal (ID) regimen, based on the Essen regimen, has been developed at the Kempegowda Institute of Medical Sciences (KIMS), Bangalore, India.

OBJECTIVE

The objective of this study was to compare the immunogenicity and local and systemic tolerability of the KIMS-1D regimen with those of the standard Essen IM regimen in healthy adult volunteers in India.

METHODS

This randomized, open-label, active-controlled trial was conductedat the Antirabies Clinic, Medical College, KIMS. Healthy adult volunteers were randomly assigned to receive purified chick embryo cell vaccine (PCECV) using the KIMS-1D regimen (0.1 mL injected ID at 2 body sites on days 0, 3, 7, 14, and 28 ["2-2-2-2-2"]) or the Essen IM regimen (1 mL injected IM at 1 body site on the same days Subjects were followed up for 365 days by the treating physician and encouraged to voluntarily report any adverse events (AEs). Serum rabies virus-neutralizing antibody (RVNA) concentrations were measured before the first injection on day 0 (baseline) and on days 14, 28, 90, 180, and 365, using the rapid fluorescent focus inhibition test.

RESULTS

Ninety-one subjects were enrolled and included in the tolerabilityand immunogenicity analyses. The ID group comprised 45 subjects (26 men, 19 women; mean [SD] age, 20.84 [1.48] years); the IM group, 46 subjects (28 men, 18 women; mean [SD] age, 21.02 [1.16] years). The most common local AEs were pain at the injection site (2/225 [0.9%] in the ID group and 10/230 [4.3%] in the IM group; P < 0.006) and itching at the injection site (5/225 [2.2%] in the ID group and none in the IM group; P = 0.026). All of the AEs were transient and resolved without the need for medication. All subjects had serum RVNA concentrations ≥0.5 IU/mL-considered protective by the World Health Organization-at all follow-up visits. However, the mean RVNA concentrations in the IM group were significantly higher compared with those in the ID group from days 14 to 365 (all, P < 0.001).

CONCLUSION

In this study in healthy volunteers, PEP with PCECV administered using the KIMS-ID regimen was well tolerated and immunologically efficacious for 365 days. Adequate RVNA levels were maintained with the KIMS-ID regimen from days 14 to 365, although these levels were significantly lower than those achieved in the group receiving the Essen IM regimen (all, P < 0.001).

Generation and characterization of the human neutralizing antibody fragment Fab091 against rabies virus

AIM

To transform the human anti-rabies virus glycoprotein (anti-RABVG) single-chain variable fragment (scFv) into a Fab fragment and to analyze its immunological activity.

METHODS

The Fab gene was amplified using overlap PCR and inserted into the vector pComb3XSS. The recombinant vector was then transformed into E coli Top10F' for expression and purification. The purified Fab was characterized using SDS-PAGE, Western blotting, indirect ELISA, competitive ELISA, and the fluorescent antibody virus neutralization test (FAVN), respectively, and examined in a Kunming mouse challenge model in vivo.

RESULTS

A recombinant vector was constructed. The Fab was expressed in soluble form in E coli Top10F'. Specific binding of the Fab to rabies virus was confirmed by indirect ELISA and immunoprecipitation (IP). The neutralizing antibody titer of Fab was 10.26 IU/mL. The mouse group treated with both vaccine and human rabies immunoglobulin (HRIG)/Fab091 (32 IU/kg) showed protection against rabies, compared with the control group (P<0.05, Logrank test).

CONCLUSION

The antibody fragment Fab was shown to be a neutralizing antibody against RABVG. It can be used together with other monoclonal antibodies for post-exposure prophylaxis of rabies virus in future studies.

Assessing the relationship between antigenicity and immunogenicity of human rabies vaccines when administered by intradermal route: results of a metaanalysis

The metadata of 10 published studies and 3 vaccine trial reports comprising of 19 vaccine cohorts from four countries conducted over a period of 23 years (1986 - 2009) was used for metaanalysis. The vaccines studied were purified chick embryo cell vaccine (Rabipur, India & Germany), purified vero cell rabies vaccine (Verorab, France; Indirab, India) & human diploid cell vaccine (MIRV, France).The potency of these vaccines varied from 0.55 IU to 2.32 IU per intradermal dose of 0.1 ml per site. The vaccines were administered to 1,011 subjects comprising of 19 cohorts and using five different ID regimens. The immunogenicity was measured by assays of rabies virus neutralizing antibody (RVNA) titres using rapid fluorescent focus inhibition test (RFFIT) [15 cohorts] and mouse neutralization test (MNT) [4 cohorts]. The statistical analysis of the data was done by Karl Pearson's correlation coefficient to measure the relationship between antigenicity and immunogenicity. It was revealed that, there was no significant linear relationship between antigenicity and immunogenicity of rabies vaccines when administered by intradermal route. (p> 0.230 and p>0.568).

Safety and efficacy of novel dermal and epidermal microneedle delivery systems for rabies vaccination in healthy adults

In the present pilot study, intradermal ID delivery systems with a BD microneedle from 1 to 3mm in length, and epidermal delivery (BD skin abrader) through abraded skin surface relative to standard intramuscular injection were evaluated. Circulating neutralizing antibodies were measured against the rabies virus after the Vero cells rabies vaccine was administered at D0, D7, D21 and D49. This clinical evaluation in 66 healthy volunteers shows that ID delivery using BD microneedle technology of 1/4 the IM antigen dose is safe, efficient and reliable, resulting in a protective seroconversion rate. In contrast, the epidermal delivery route did not produce an immune response against the rabies vaccine.