Immunogenicity of anti-rabies vaccines (ARVs) marketed in Sri Lanka: a comparative study.

Several brands of anti-rabies vaccines (ARVs) are used for dog vaccination in Sri Lanka, which have shown major differences in their potency levels. This comparative study was conducted to determine humoral immune response of these ARVs using 2 different animal species. The reliability of an enzyme-linked immunosorbent assay (ELISA) antibody kit was assessed in comparison to the standard Fluorescent Antibody Virus Neutralization (FAVN) test. The laboratory animal study was conducted using 3-4 months old sero-negative New Zealand White rabbits. Nine vaccines from 7 producers were tested including 8 monovalent inactivated ARVs: Canvac R® single-dose and multi-dose, Nobivac® Rabies, Rabies Killed® Vaccine, Rabisin®, Defensor 3®, Raksharab® single-dose and multidose, and one bivalent inactivated ARV, Nobivac® RL. Second part was conducted in field dogs. Four vaccines with the highest potencies were selected for this field dog study. Animals were vaccinated subcutaneously with one dose of a selected ARV. Day 0 blood samples were collected just before the vaccination and Day 7, Day 14, and Day 30 samples from rabbits and Day 30 samples from dogs were collected post-vaccination. Significant differences of humoral immune response between different vaccines brands were observed in both animal species. The coefficient of concordance between the FAVN test and the ELISA was 54.6% and 85.3% for rabbits and dogs respectively. The overall results showed that ARVs with proven potency can induce a robust humoral immune response following vaccination. There was a comparatively higher agreement between the FAVN test and the ELISA.