Evaluation of a feline leukemia virus vaccine in a controlled natural transmission study.

Twenty-six 8-week-old specific-pathogen-free cats were vaccinated subcutaneously with 2 doses of a commercially available FeLV vaccine, and 26 age-matched specific-pathogen-free cats were similarly vaccinated with a placebo vaccine containing the same adjuvant as the FeLV vaccine. Cats then were randomly assigned to 2 groups of 26 cats (13 FeLV-vaccinated cats and 13 control cats), and each group was housed with 5 cats previously inoculated with FeLV. All cats were tested biweekly for the next 26 weeks for evidence of FeLV antigenemia. Five of the 26 control cats developed antigenemia. However, 4 of these cats were only transiently antigenemic (positive results for 3 consecutive biweekly samples) and only 1 was persistently antigenemic. None of the FeLV-vaccinated cats developed antigenemia. Preventable fraction was calculated to be 100%.