|In general, avoid using any medications, drugs, or vaccines in pregnant or lactating (producing milk) animals. Any vaccine component that is modified live could conceivably cross the placenta and cause defects or deaths of the fetuses. This is known to be true in non-immune cats vaccinated with a modified live panleukopenia vaccine during pregnancy. Some vaccines, however, have been tested in pregnant or lactating animals and can be used in circumstances in which the animal does not have immunity to a specific disease and needs to be immunized. If vaccination must occur, use a killed vaccine. Your veterinarian will be able to help you determine which vaccines can or should be given to your pregnant animal.
Vaccinating a lactating animal will not provide protection to her nursing offspring. The mother's immune system will take at least a week to react to the vaccine and produce higher levels of antibody. And remember, the newborns can only receive antibodies from their mother through the colostrum in the first 36 hours of their lives. By the time the mother's antibody level has increased, the offspring will no longer be able to absorb them. The vaccination, then, may help protect the mother, but it will not provide antibody protection to her nursing offspring.