Puppies and Kittens Need More than One Vaccine Against Viral Infections

The first two days after giving birth, the mother produces a special milk called colostrum. This milk contains the mother’s antibodies against all the viral infections she has experienced or been immunized for, and until these antibodies decrease to ineffective levels, they will protect the puppy or kitten. However, these antibodies will also inactivate any vaccine given to the puppy or kitten.

A vaccine solution contains a harmless version of the virus, either live and weakened (attenuated or modified live virus vaccine) or killed (inactive virus vaccine). If a vaccine is injected into the puppy or kitten and there is still adequate maternal antibody present, the vaccine virus will be destroyed just as if it were a real viral infection. There will be a period of about week when there is not enough maternal antibody to the protect the puppy or kitten but too much to allow a vaccine to work (this period is called the window of vulnerability). After this period, vaccines can be effective. To get around this, we vaccinate puppies or kittens in a series. Giving a vaccine every two (2) to four (4) weeks from the ages of six (6) weeks until the age of 16 weeks.

By giving a vaccine at intervals we are trying to catch the puppy or kitten’s immune system after their window of vulnerability has closed. We know that by the age of 16 weeks, we should be able to get a vaccine to take effect, but we still begin at a younger age in effort to provide immunization as soon as possible. This method is proven to be the most effective at protecting individual animals as well as increasing “herd” immunity.

If the mother has been well vaccinated (booster vaccine given at approximately the time of breeding so as to maximize her colostral antibodies), an extra vaccine dose for the puppy or kitten at 20 weeks of age may be a good idea to be sure all the maternal antibodies have waned adequately.

Once the puppy or kitten has reached 16 weeks of age and has had all their shots, they should receive booster vaccine once a year or based on a veterinarian’s recommendations.