Evaluation of two intradermal vaccination regimens using purified chick embryo cell vaccine for post-exposure prophylaxis of rabies.

BACKGROUND: Post-exposure prophylaxis for rabies with cell culture vaccines by the conventional intramuscular regimen is very expensive. The World Health Organization has advocated two cost-effective intradermal regimens with cell culture vaccines for use in developing countries. We evaluated these two regimens--the 2-site and the 8-site regimens--in terms of immunogenicity, safety and tolerance in people with category I exposure to rabies. METHOD: Eighty-two subjects who had mild category I exposure to rabies were immunized using a purified chick embryo cell vaccine. The first regimen given to 43 subjects, consisted of intradermal administration of 0.2 ml of vaccine at 2 sites on days 0, 3 and 7 and at one site on days 28 and 90. The second regimen, given to 39 subjects, consisted of intradermal administration of 0.1 ml of vaccine at 8 sites on day 0, at 4 sites on day 7 and at one site on days 28 and 90. The mouse neutralization test was used to estimate titres of rabies neutralizing antibody in these subjects on different days after vaccination. The subjects were followed up for 1 year. RESULTS: Both regimens produced adequate neutralizing antibody titres from day 14 onwards, though the second regimen produced a more rapid antibody response and significantly higher titres (p < 0.001) on all days tested. There were minimal side-effects and both regimens were well tolerated. CONCLUSION: Both the 2-site and 8-site intradermal regimens with purified chick embryo cell vaccine produce adequate levels of neutralizing antibodies but the 8-site regimen appears to be more immunogenic. The feasibility of using these cost-effective regimens in routine practice needs to be further evaluated under the field conditions prevalent in India.