Animal Medical Hospital

2459 Bellevue Avenue
West Vancouver, BC V7V 1E1


Should Your Pet Be Shot?
The Pet Vaccination Controversy

Cathy Wilkie, DVM

Feline vaccinations and duration of immunity

Aggregate of studies

Duration of

Study type

Feline herpes virus

7+ years


Feline calici virus

7+ years


Feline panleukopenia virus

7+ years


Feline leukemia virus

Preliminary study
3 years


Rabies virus

7 years


It should be noted that vaccination against the upper respiratory viruses (herpes, calici) rarely confers absolute protection against infection. Rather, they protect against severe disease. Vaccinated cats can and do get upper respiratory virus infections, but they tend to be milder than they otherwise would be, and are generally self-limiting. Upper respiratory vaccines can cause mild signs of disease, especially the intranasal vaccine. As with the canine vaccines, there is not 100% protection for 100% of cats for most vaccines. In the case of feline vaccines, panleukopenia vaccination seems to confer the strongest immunity each study showed 100% protection even after 7 years. There are, however, a limited number of cats in each study. Statistically, if the study sample size were large enough, there would likely be a certain small percentage of cats who, after 7 years, were not protected. Still, this vaccine seems to give excellent protection, in many cases even after a single dose.

The feline leukemia virus study was an extreme challenge study. The cats involved were all positive for feline immunodeficiency virus (FIV), the cat equivalent of HIV. They were vaccinated once, and housed permanently with FeLV-infected cats. Three years later they were tested; none of these cats became FeLV positive. At the same time (3 years after vaccination), they were injected intra-abdominally with a large dose wild-type feline leukemia virus. 93% remained negative, and the remaining 7% seroconverted (had circulating virus after exposure) but became negative again within 3 months. This challenge is considered extreme because the amount of virus used for the challenge far exceeded what would reasonable be expected in a real exposure, it was given by a route that would have caused immediate, severe infection in an un-immunized cat, and also because these cats were immunocompromised to varying degrees by the FIV infections they harbored. Still, they were able to overcome the infection.

There is good evidence that there is a large degree of age-related resistance to FeLV infection. It is difficult to infect cats over 6 months of age. So difficult, in fact, that most of the studies of FeLV infection are done on kittens, as the researchers find it impossible to reliably infect an adequate number of adult cats.






Animal Medical Hospital

2459 Bellevue Avenue

West Vancouver, BC
V7V 1E1
Tel: 604-926-8654
Fax: 604-926-6839

Animal Medical Clinic on Georgia

1338 West Georgia Street

Vancouver, BC
V6E 4S2
Tel: 604-628-9699
Fax: 604-926-6839

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