The basic principle of vaccination was discovered by an English scientist, Edward Jenner, in 1796. He saw that the girls who milked cows often got cowpox, and that seemed to make them immune to a more serious disease, smallpox. From these humble beginnings did develop the wide array of modern vaccinations that are available to our pets today.
The first step in making a vaccine is to identify and isolate the disease’s causative organism. Usually a virus, it is then weakened or killed until it is safe to be given to the susceptible individual. With a normally functioning immune system, the body can then figure out how to produce protective substances called antibodies which specifically attack and neutralize the virus. When a booster vaccination is given at a later date, the immune system is reminded that it has already been exposed to this germ and is able to produce more antibody, more rapidly and more efficiently.
When the real disease comes along the immune system is ready and is capable of destroying the challenging virus. This kind of immunity is called active immunity.
When puppies and kittens start getting vaccinated at eight weeks of age, they usually receive a series of vaccinations. Why is this necessary? It has to do with a process called maternal interference. Unlike people, puppies and kittens receive virtually no antibodies from their mothers while in the uterus. They obtain all their antibodies from nursing during the first twenty-four hours of life. After twenty-four hours, the intestine stops absorbing the antibodies and starts digesting them. This is why it is critical for nursing to occur! The absorption of the antibodies produces a passive immunity– meaning that these antibodies are on loan only, the body is not actively producing them. Because of this, the passive immunity will last only a few weeks. There is always a two week period between eight and sixteen weeks, where the level of passive immunity is too high to allow the vaccination to work but yet is too low to protect the individual from the disease, even if we administered a vaccine every day!! For this reason, it is recommended that while the puppy or kitten is undergoing its initial series of vaccinations, it should not be exposed to areas of public access. Stray dogs and cats are the main reservoirs of dog and cat distemper as well as canine Parvo and feline leukemia viruses. The worst places to take a new puppy or kitten are the parks and beaches as well as on public streets. It is ok to take them to a friend’s house or have their pets visit your home as long as you know the health and vaccination status of these pets.
Recently, there has been much discussion in the veterinary community regarding how frequently booster vaccinations should be given. When the original guidelines were established thirty some years ago it was decided to advise annual vaccinations. This philosophy catered to the lowest common denominator theory. This school of thought felt that the frequency of the boosters should be based on the animals that had the weakest immune response to the vaccine- that is, if ten percent of those vaccinated only maintained immunity for a year, then in lieu of testing each dog for its antibody level, all individuals were advised to get yearly vaccines. Now the philosophy seems to be changing and many of us in the veterinary profession are expecting to see revised vaccination schedules which call for boosters every two to three years. The cost of testing for antibody levels has decreased dramatically (although it is still three to four times as expensive as the vaccine) and it is now feasible to run antibody assays especially for those pets who have had previous adverse vaccination reactions or whose immune system has been suppressed through disease.
Consult your local veterinarian for professional advice as to what vaccinations are appropriate for pets in your area — both the type(s) and frequency of vaccinations that will benefit your particular pet.
Dr. Baum has been the owner and Chief of Staff at Center-Sinai Animal Hospital, Los Angeles, California since 1979. The hospital has been serving the Los Angeles community for over thirty years.