Evaluation of Antibody Response in Horses After Vaccination With an Inactivated Getah Virus Vaccine Using an Accelerated Immunization Schedule

Abstract

Antibody response in horses after accelerated-schedule Getah virus vaccination was evaluated for its potential adoption during outbreaks. One-year-old Thoroughbred horses received two doses of priming vaccinations following an accelerated schedule (accelerated group: 14-day interval, n = 30) or the conventional schedule (control group: 28-day interval, n = 30). At Day 14, both groups showed similar seropositive rates (66.7% in control group and 73.3% in accelerated group) and geometric mean (GM) virus-neutralizing titers (5.2 [95% confidence interval (CI), 3.0–8.8] in control group and 5.3 [95% CI, 3.1–8.9]). At Day 28, the controls showed a lower seropositive rate (40.0%) and GM titer (2.2 [95% CI, 1.5–3.3]), whereas these figures were significantly higher in the accelerated group, at 80.0% and 7.0 (95%CI, 4.2-11.6, P < .05). The control group's antibody response peaked on Day 42, with a seropositive rate of 80.0% and GM titer of 11.3 (95% CI, 5.6–24.0). From Day 42, the accelerated group showed a faster decline in seropositive rate and GM titer than the control group. Despite the relatively short persistence of antibodies after a second vaccination, the accelerated vaccination schedule proved effective in bridging the detrimental immunity gap that is observed in conventionally vaccinated horses, suggesting the potential usefulness of this accelerated vaccination schedule as an emergency control measure.