Why Do Baby Animals Need a Series of Shots and How Many do They Need?

When a kitten or puppy is born, its immune system is not yet mature; the baby is wide open for infection. Fortunately, nature has a system of protection. The mother produces a certain kind of milk in the first few days after giving birth. This milk is called colostrum and is rich in all the antibodies that the mother has to offer. As the babies drink this milk, they will be taking in their mother's immunity. After the first couple of days, regular milk is produced and the baby's intestines undergo what is called closure, which means they are no longer able to take externally produced antibodies into their systems. These first two days are critical to determining what kind of immunity the baby will receive until its own system can take over.

How long this maternal antibody lasts in a given puppy or kitten is totally individual. It can depend on the birth order of the babies, how well they nursed, and a number of other factors. Maternal antibodies against different diseases wear off after different times. We DO know that by 14-20 weeks of age, maternal antibodies are gone and the baby must be able continue on its own immune system.

While maternal immunity is in the puppy or kitten’s system, any vaccines given will be inactivated. Vaccines will not be able to "take" until maternal antibody has sufficiently dropped. Puppies and kittens receive a series of vaccines ending at a time when we know the baby's own immune system should be able to respond. We could simply wait until the baby is old enough to definitely respond, as we do with the rabies vaccination, but this could leave a large window of vulnerability if the maternal antibody wanes early. To give babies the best chance of responding to vaccination, we vaccinate every 2-3 weeks during this period, in hope of gaining some early protection.

When a vaccine against a specific disease is started for the first time, even in an adult animal, it is best to give at least two vaccinations. This is because the second vaccination will produce a much greater response if it is following a vaccine given 2-3 weeks prior.

What Do I Do if My Pet Skips a Year of Vaccination?

It depends on the vaccine. Here are the recommendations for adult animals who skip an annual vaccine:

  • Feline distemper (FVRCP) - Vaccinate normally. It is not necessary to re-start the initial series.
  • Feline leukemia (FeLV) - If an adult cat has skipped an annual booster, it is not necessary to restart the initial series and vaccination can simply pick up where it left off.
  • Rabies - A three-year vaccine can be given any time after the initial one-year vaccine as long as there is proof the vaccine has been given. This means that if a year is skipped, the next rabies vaccine given will still be a three-year vaccine. One-year vaccines can be boosted at any time and will be good for one year from the time they are given.
  • Canine distemper, canine parvovirus, nasal Bordetella - Vaccinate normally. You do not need to restart the initial series as though the pet is starting over from the beginning.
  • Canine Influenza - The series should be restarted if longer than 2 years have passed since the last dose.
  • Canine Leptospirosis - The series should be restarted If longer than 2 year have passed since the last dose.
  • Lyme disease - Should a dog in a geographically affected area skip a year with this vaccine, it is recommended restarting the initial series.