Immunogenicity of two modern tissue culture rabies vaccines in pre-exposure prophylaxis

Pre-exposure prophylaxis was given to employees supposed to be involved in rabies vaccine production in India. Prior to availability of the manufacturer's own human diploid cell (HDC) vaccine (Rabivax((R))), immunization was executed with a chick embryo cell (CEC) vaccine (Rabipur((R))). This constellation gave an opportunity to compare retrospectively immunogenicity of these two vaccines. The data was collected by retrospective analysis over more than three years at the clinic of Serum Institute of India Ltd. As per the standard protocol, persons with negative rabies vaccination history receive a dose of 1 ml of rabies vaccine intramuscularly on day 0, 7 and 28, and the virus anti-glycoprotein antibodies are measured one month after the third dose. The antibody levels >= 0.5 IU/ml are considered protective. The CEC and HDC vaccines were used during the analysis period. In all, 43 individuals received the CEC vaccine, 106 the HDC vaccine. The mean age of recipients was 33 years five months (Rabipur((R))) and 30 years three months (Rabivax((R))). All subjects in both groups were males. Five commercial batches of the CEC vaccine (129 doses) and seven batches of the HDC vaccine (318 doses) were used. Ninety-nine percent of the HDC and 93% of the CEC vaccine recipients were protected after the standard three dose schedule. Geometric mean titre was significantly greater for the HDC than CEC vaccine, being 5.05 IU/ml and 2.90 IU/ml, respectively (p = 0.0002). The HDC vaccine showed a good lot-to-lot consistency with respect to GMT both by ANOVA test and Nonparametric ANOVA test. On the other hand, the CEC vaccine demonstrated a variation in titres, when the lots were compared. Three out of four low-responders accepted a booster vaccination, and regardless of whether Rabipur((R)) or Rabivax((R)) was used, all three responded well one month after the booster. The Indian HDC vaccine compares well with the CEC vaccine in terms of immunogenicity. With HDC vaccines, cost has been an issue. However, since the new HDC vaccine has a comparable cost to the CEC vaccine, it may be possible to use it in large-scale vaccinations.