Evaluating triple inactivated vaccine-induced immunity from a large-scale study in feline population

Feline panleukopenia virus (FPV), feline calicivirus (FCV), and feline herpesvirus-1 (FHV-1) substantially impact feline health. Field evidence on vaccine-induced population immunity remains limited. We evaluated humoral responses in 4,736 vaccinated domestic cats across 24 provinces in China (July 2024-June 2025), quantifying neutralizing antibody titers to FPV, FCV, and FHV-1 after a trivalent inactivated vaccine (Meowonder™). For cats aged 3 months or older, two primary doses achieved high antibody positivity rates across pathogens; a third dose yielded marginal additional benefit, while boosters-maintained titers. Antibody peaks occurred in late summer and early winter, with a decline beginning in February and a rebound in spring. Maternal-derived antibodies (MDAs) interfered most in kittens < 4 months. A subset with very high FPV titers but sub-threshold FCV/FHV-1 titers had recent environmental FPV based on pet owners' feedback. The variability of individual immune responsiveness, potentially influenced by feline leukocyte antigen (FLA) polymorphisms, likely contributed to heterogeneous responses. These results support a two-dose primary series for cats aged ≥ 3 months, followed by periodic boosters, emphasizing the importance of vaccine schedules and consideration of genetic and environmental factors for effective disease management.