A serological survey was performed on dogs vaccinated in the field with four brands of inactivated adjuvanted rabies vaccines. Eight hundred thirty-seven Philippine native dogs were vaccinated from December 1990 to June 1992. The dogs were separated into four groups (A, B, C, and D) corresponding to the brand of vaccine used. Blood samples were taken on the day of vaccination and 30, 180, and 360 days after vaccination. There was a total of 713 dogs available at 30 days, 507 at 6 months, and 400 serum samples at 1 year. The last samples were extracted on June 1993. The geometric mean titer (GMT) (at 30 days post-vaccination) of dogs vaccinated with vaccine A was 11.01 IU/mL; with vaccine B, 4.01 IU/mL; with vaccine C, 12.26IU/mL; and with vaccine D, 1.42 IU/mL. At 180 days, the GMT dropped to 1.63 IU/mL in vaccine A, 1.07 IU/mL in vaccine B, 1.48 IU/mL in vaccine C, and 0.55 IU/mL in vaccine D. The seroconversion rate increased on day 30 and decreased on day 180. Most (99.96%) of the dogs immunized with vaccine A had serum titers greater than or equal to 0.5 IU/mL. In the other groups, 98.21% of the dogs immunized by vaccine B, 100% of the dogs immunized by vaccine C; and 85.28% of the dogs immunized by vaccine D had serum titers greater than or equal to 0,5 IU/mL. However, at 180 days, the number of dogs with greater than or equal to 0.5 IU/mL dropped to 88.24% with vaccine A, 77.95% with vaccine B, 92.65% with vaccine C, and 58.33% with vaccine D. The possibility of certain factors such as nutrition, pollution, climate, and other factors affecting the immune response of the dogs with low serum titer has not been established.
