A comparative study on the immunogenicity, safety and tolerance of purified duck embryo vaccine (PDEV) manufactured in India (Vaxirab) and Switzerland (Lyssavac-N): a randomized simulated post-exposure study in healthy volunteers.

Purified duck embryo vaccine (PDEV, Vaxirab) for rabies prophylaxis is now indigenously manufactured in India under technology transfer from Berna Biotech who made the original PDEV (Lyssavac). In the present study we have compared the two vaccines in terms of safety, immunogenicity and tolerance. The study was conducted in 220 adult healthy volunteers. It was observed that both vaccines produced neutralizing antibody titers (as determined by rapid fluorescent focus inhibition test, RFFIT) more than 0.5 IU/mL (minimum level for seroconversion) on all days tested but the titers on days 90 and 180 were significantly higher with Lyssavac. The adverse reactions produced were slightly more with Lysssavac but both vaccines were well tolerated. In conclusion, the indigenously produced PDEV (Vaxirab) was found to be equally safe and immunogenic as the original PDEV (Lyssavac) manufactured at Switzerland.

Use of neutralizing murine monoclonal antibodies to rabies glycoprotein in passive immunotherapy against rabies.

Passive immunization is an important parameter of post exposure rabies prophylaxis. Two types of rabies immunoglobulin (RIGs) are currently available for Passive immunization against rabies i.e., human rabies immunoglobulin (HRIG) and equine rabies immunoglobulin (ERIG). The former is very expensive and not easily available and the latter causes side effects because of which its utility is limited. In the present study we have produced murine monoclonal antibodies (Mabs) to rabies glycoprotein (G) and studied their utility in passive immunization against rabies using animal models. Their efficacy was compared to commercially available ERIG both in terms of neutralizing titer and effective protein concentration. The neutralizing titers of these Mabs ranged from 1650-75,000 IU/mL by RFFIT. They belonged to the IgG 2 a subclass. The Mabs were able to protect 70-100% of mice and guinea pigs inoculated with rabies viruses, depending on the strain of the virus. These Mabs were found to be 2,000 times more potent than commercial ERIG in terms of effective protein concentration and neutralizing titer. Further studies are required to study their utility in humans exposed to rabies.

Development and evaluation of a competitive ELISA for estimation of rabies neutralizing antibodies after post-exposure rabies vaccination in humans.

OBJECTIVES: Currently three tests are approved for the estimation of neutralizing antibodies after rabies vaccination: the mouse neutralization test (MNT), the rapid fluorescent focus inhibition test (RFFIT), and the fluorescent antibody virus neutralization (FAVN) test. Performance of these tests requires a lot of expertise and is generally carried out in reference laboratories and, hence, they are not available to many people. The aim of the present study was to develop and evaluate a competitive ELISA (C-ELISA) for estimation of neutralizing antibodies in order to make this testing more widely available. METHODS: The C-ELISA was designed based on competition between a murine neutralizing monoclonal antibody (Mab) and the antibodies in serum of vaccinated people. The test was initially standardized using known negative and known positive serum samples for determining the optimal dilution of the Mab as well as the cut-off value (%) for ascertaining the level of inhibition. Nine hundred and ninety serum samples were tested from 250 people who had been administered purified chick embryo cell vaccine (PCECV). Serum samples were collected on days 0, 14, 30 and 90 post-vaccination, and were tested by C-ELISA. RESULTS: All the serum samples that were positive by RFFIT were also positive by C-ELISA. The titers obtained with C-ELISA were marginally higher than the RFFIT titers, but a significant correlation was noted between the two tests (r=0.897). None of the negative controls were detected to be positive for rabies antibodies by either of these tests. Therefore the C-ELISA was found to be 100% specific and sensitive in comparison to RFFIT. Further, the initial rise and fall of antibody titers on different days post-vaccination was comparable for both tests. CONCLUSIONS: The C-ELISA described herein can be used to quantify rabies neutralizing antibody levels after vaccination. This test is simple and can be conveniently used under field conditions for monitoring seroconversion after post-exposure rabies vaccination. Moreover it does not require handling of infectious virus by the end user.

Comparison of saftey and immunogenicity of purified chick embryo cell rabies vaccine (PCECV) and purified vero cell rabies vaccine (PVRV) using the Thai Red Cross intradermal regimen at a dose of 0.1 ML.

Intradermal (ID) vaccination with modern cell culture rabies vaccines is a means to significantly reduce the cost of post-exposure prophylaxis as compared to intramuscular vaccination. In this study we evaluated the efficacy, immunogenicity and tolerability of PCECV and PVRV administered ID in doses of 0.1 mL per site according to the 2-site Thai Red Cross (TRC) regimen. Patients with WHO category III exposure to suspect or laboratory proven rabid animals were administered either PCECV (n = 58) or PVRV (n = 52) ID at a dose of 0.1 mL per site at two sites on days 0, 3 and 7 and at one site on days 30 and 90. Serum samples were withdrawn on days 0, 14, 30, 90 and 180 and rabies virus neutralizing antibody (RVNA) titers were determined by rapid fluorescent focus inhibition test (RFFIT). Patients who were exposed to laboratory confirmed rabid animals were followed up for one year after exposure. All 110 patients developed RVNA titers above 0.5 IU/mL by day 14. Adequate titers >0.5 IU/mL were maintained up to day 180. Both vaccines induced equivalent RVNA titers at all time points and were well tolerated. Five subjects who were bitten by laboratory confirmed rabid dogs were alive and healthy one year after exposure. As demonstrated, PCECV and PVRV are both immunogenic, efficacious and well tolerated when administered in the TRC post-exposure prophylaxis regimen in ID doses of 0.1 mL as recommended by WHO guidelines. The use of PCECV in this regimen may prove more economical in developing countries like India.