With the increase of fibrosarcomas in cats and an epidemiologic link between vaccination and the tumors, recommendations for annual vaccination of cats have changed. Historically, veterinary vaccinations approved by the U.S. Department of Agriculture have been granted 1-year booster recommendations, although maximum duration of immunity has not been established (except in the case of rabies vaccines). This study used client-owned cats that were more than 2 years of age and had previously been vaccinated with feline panleukopenia virus (FPV), feline calicivirus (FCV), and feline herpesvirus (FHV). The 272 cats were of various ages, genders, breeds, weights, and lifestyles. They all had negative FeLV and FIV testing results on day 0 and had received a 2-dose primary vaccination series with a vaccine from the same line as the test vaccine (Felocell 4-Pfizer Inc, New York, NY). A blood sample for serum titer was taken before vaccination of the cats and again 5 to 7 days later. The time since last vaccination (TSLV) ranged from 12 to more than 48 months. In most cats, the primary vaccination had induced a response that lasted up to and beyond the 48 months. In this study, revaccination with the same vaccine caused a significant anamnestic response in most TSLV groups. This study suggests, on a vaccine-specific basis, that a rationale of revaccination intervals longer than 1 year may be appropriate. Funding for this study was provided by Pfizer Animal Health, New York, NY.

COMMENTARY: This study involving 272 healthy client-owned cats is germane at this time given the ongoing controversies regarding vaccine intervals in cats. Results revealed that cats either maintained a titer above the threshold or responded to vaccination with equal to or greater than a fourfold increase. Although this study is not equivalent to challenge-of-immunity studies, it does show that revaccination with the same vaccine provides significant titers well beyond one year.

Duration of serologic response to three viral antigens in cats. Mouzin DE, Lorenzen MJ, Haworth JD, King VL. JAVMA 224:61-66, 2004.