Research| Veterinarian Awareness

Are Vaccines Worth It?

(Opinion piece by Christine Wilford, DVM reprinted with permission from Compassionate Solutions: Journal of the Feral Cat Spay and Neuter Project’s Spring 2009 edition; originally from November 2004 Feral Cat Times)

A well-respected, national rescue organization recently stated a great falsehood that vaccinating feral cats with FVRCP, the “distemper” (panleukopenia) and respiratory virus vaccine, was useless and not recommended. That is simply not true. Here are the facts:

There are two basic types of FVRCP vaccines: killed virus (KV) and modified live virus (MLV). To get immunity from killed virus vaccines, at least two doses are required. KV vaccines prime the immune system for creating protective immunity after a subsequent booster. The first dose shows the body the enemy and a second dose is given to generate protective immunity. Paired doses are required 3-5 weeks apart. Using killed virus vaccines for free-roaming cats is clearly undesirable, because giving boosters is impractical.

On the other hand, MLV vaccines begin stimulating immunity the first day they are given. The vaccine contains viruses that replicate in the cat’s body but do not cause disease. A booster 3-4 weeks later is never required nor recommended in cats over 14 weeks of age. Another benefit is that vaccinated cats can shed attenuated vaccine virus particles in the feces. These viruses do no harm, and actually stimulate immunity in other cats/kittens coming in contact with the feces. This is potentially valuable in colonies of free-roaming cats.

The only caution with MLV vaccines is hygiene. If the vaccine accidentally gets ON the cat instead of IN the cat, then it may cause some mildly runny eyes or mild sneezing. Vaccine virus cannot cause symptoms of distemper. MLV vaccine that gets topical should be cleaned off with a swab of alcohol.

Kittens under 14 weeks of age have varying levels of immunity from antibodies passed from their mother. Early in kittenhood, antibody levels are highest. As the weeks pass, antibodies gradually decline. For several weeks, antibody levels drop too low to protect from disease but remain too high to allow a vaccine to work. The antibodies “fight off” the vaccine. Known as the “critical period” or “vulnerable period” between 6-12 weeks, this stage of uncertainty is why tame kittens are vaccinated every 3-4 weeks until after 14 weeks of age. Vaccines given at the earliest point where the body can respond shortens the period that the kittens are vulnerable to diseases. By 14 weeks of age, the mother’s antibodies wear off enough to allow the vaccine to work. Therefore, any normal kitten over 14 weeks can receive one MLV vaccine and not need a booster.

So when considering vaccines, MLV vaccines can be effective with one injection. Do we recommend them for feral cats? That depends. NOT if it means less money available for surgeries. If your money is plentiful, then consider vaccinating. If money is limited, invest it in surgery. Dollar for dollar, spay/neuter is a better investment for the cat’s health and for the futures of many, many cats.