Vaccination with an inactivated canine influenza H3N2 virus vaccine is safe and elicits an immune response in cats

Objectives: The aim of this study was to evaluate safety and seroconversion when an inactivated H3N2 canine influenza virus (CIV) vaccine was administered to cats.

Methods: Twenty 7-8-week-old seronegative cats were randomly assigned to two groups of 10 animals each. Cats in treatment group T01 were subcutaneously administered two doses of an adjuvanted placebo 3 weeks apart to serve as non-immunized controls. Cats in treatment group T02 were subcutaneously administered with two doses of H3N2 CIV vaccine at 3 weeks apart. All animals were actively monitored for 5 days after each injection for local and systemic reactions. Tympanic temperatures were recorded the day before and 5 days after each vaccination. Blood samples for serology were collected prior to each vaccination (days -1 and 20), and 7 and 14 days post-second vaccination.

Results: Minor vocalization was observed in both control and vaccinated animals after the first and second dose administration. The only injection site reaction observed was mild swelling in one control cat, which resolved within 24 h. Transient fevers (39.5-39.7^°C) that resolved within 24 h post-injection were observed in both treatment groups (T01 = 3/10 and T02 = 5/10). All vaccinated, but no control, animals successfully seroconverted within 14 days of second vaccination, with H3N2 CIV-specific hemagglutination inhibition (HAI) titers ranging from 32 to 128.

Conclusions and relevance: Cats vaccinated subcutaneously with an inactivated H3N2 CIV vaccine had similar rates of adverse events post-vaccination as the control group. Increased HAI titers provided evidence of post-vaccination seroconversion with the H3N2 CIV-vaccinated group.