Antibody Response to Feline Calicivirus Vaccination in Healthy Adult Cats

This study evaluated the prevalence of feline calicivirus (FCV) antibodies and response to vaccination in healthy adult cats. Cats >1 year (n = 111) that had not been vaccinated within 12 months of enrollment in the study received a vaccine containing inactivated FCV antigen strains 431 and G1. Antibodies were determined on Days 0, 7, and 28 by virus neutralization (VN) using FCV isolate KS20, and by broad spectrum blocking FCV enzyme-linked immunosorbent assay (ELISA). Factors associated with the presence of antibodies and vaccine response were determined by uni- and multivariate analysis. Pre-vaccination antibodies were detected in 62.2% of cats (CI(95%): 52.9–70.1) by VN and in 77.2% (CI(95%): 67.5–84.6) by ELISA. A ≥4-fold titer increase after vaccination was observed in 13.6% (CI(95%): 8.3–21.4) of cats with VN and 33.7% (CI(95%): 24.5–44.5) with ELISA. Factors associated with the presence of pre-vaccination VN antibodies were age (≥2 years; OR: 7.091; p = 0.022) and lack of previous vaccination (OR: 3.472; p = 0.014). The presence of pre-vaccination ELISA antibodies was associated with time since last vaccination (OR: 5.672; p = 0.043). Outdoor cats were more likely to have a ≥4-fold ELISA titer increase (OR: 5.556; p = 0.005). Many cats had pre-vaccination FCV antibodies, and their presence depended on previous vaccinations and increases with age. A ≥4-fold titer increase was rarely observed and was influenced by the lifestyle of the cat.