Immunogenicity of an anti-clade B feline immunodeficiency fixed-cell virusvaccine in field cats

Attempts at vaccine development for feline immunodeficiency virus (FM have been extensive, both because this is a significant health problem for cats and because FIV may be a useful vaccine model for human immunodeficiency vi rus. To date, only modest success, producing only short-term protection, ha s been achieved for vaccine trials in controlled laboratory settings. It is unclear how relevant such experiments are to prevention of natural infecti on. The current study used a vaccine that employs cell-associated FIV-M2 st rain fixed with paraformaldehyde. Subject cats were in a private shelter wh ere FIV was endemic, a prevalence of 29 to 58% over an 8-year observation p eriod. Cats roamed freely from the shelter through the surrounding countrys ide but returned for food and shelter. After ensuring that cats were FIV ne gative, they were immunized using six doses of vaccine over a 16-month peri od and observed for 28 months after the initiation of immunization. Twenty- six cats (12 immunized and 14 nonimmunized controls) were monitored for a m inimum of 22 months. Immunized cats did not experience significant adverse effects from immunization and developed both antibodies and cellular immuni ty to FIV, although individual responses varied greatly. At the conclusion of the study, 0 of 12 immunized cats had evidence of FIV infection, while 5 of 14 control cats were infected. Thus, the vaccine was safe and immunogen ic and did not transmit infection. Furthermore, vaccinated cats did not dev elop FIV infection in a limited clinical trial over an extended time period . Thus, the data suggest that a fixed, FIV-infected cell vaccine has potent ial for preventing natural FIV infection in free-roaming cats.