Open Access Open Badges Research article

Difficulties in demonstrating long term immunity in FeLV vaccinated cats due to increasing age-related resistance to infection

Stephen Wilson1*, Juliet Greenslade2, Gillian Saunders1, Catherine Holcroft2, Lynn Bruce2, Andy Scobey3, Tedd Childers3, Gordon Sture3 and James Thompson3

Author Affiliations

1 Veterinary Medicine Research and Development, Pfizer Animal Health, Pfizer European Service Centre, Zaventem, Belgium

2 Veterinary Medicine Research and Development, Pfizer Animal Health, Ramsgate Road, Sandwich, UK

3 Pfizer Animal Health, Portage Road, Kalamazoo, USA

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BMC Veterinary Research 2012, 8:125  doi:10.1186/1746-6148-8-125

Published: 28 July 2012



Feline leukaemia virus (FeLV) is a pathogen causing fatal illness in cats worldwide, and as such there is a high demand for products to protect against disease. The duration of immunity provided by an inactivated FeLV vaccine, Versifel FeLV, when administered to cats of the target age was determined. Kittens received two vaccinations when aged 7 to 9 weeks old, and were subsequently challenged up to 36 months later with the FeLV-A Glasgow isolate.


In all studies, all of the younger aged control kittens showed persistent FeLV p27 antigenaemia confirming that the challenge virus was severe and efficacious. In contrast, the control cats did not show the required level of persistent antigenaemia, with a maximum of 45% cats affected in the middle duration study and only 10% in the longer study. However, apart from one animal in the short duration study, all of the cats vaccinated with Versifel FeLV were negative for persistent antigenaemia and can be considered treatment successes.


In conclusion, we have shown that although age-related resistance to infection with a virulent FeLV challenge is evident from as early as 10 months of age, vaccination with Versifel FeLV may aid in the protection of cats from FeLV related disease up to three years after primary vaccination as kittens.

Feline; Leukaemia; Vaccine; Protection