Vaccines provide protection to a large number of individuals in a population, thereby preventing spread and reducing severity of disease. Vaccines have proven to be highly effective in the control of animal diseases such as rabies, parvo-viral infection, and canine and feline distemper.
Shortly after puppies and kittens are born, they receive concentrated antibodies in “colostrum” from their mother’s milk. Antibodies are proteins that can bind and inactivate viruses, toxins and other invaders. If a mother has adequate immunity, she will likely transfer adequate protective antibodies to her young. However, not all mothers have high antibody levels, and not all puppies and kittens absorb them well in those critical first few days. Furthermore, these antibodies wane as the babies grow, usually disappearing entirely by 16-20 weeks of age.
When we vaccinate young animals, we are trying to stimulate their developing immune systems to produce antibodies against common diseases. Because the antibodies they receive from their mothers can interfere and inactivate the vaccinations, we need to repeat the vaccines until the maternal antibodies have completely disappeared. We typically begin vaccines on young puppies and kittens at about 7-8 weeks of age, and continue these every 3-4 weeks up to 16 weeks of age.
In order for young dogs and cats to have the best immunity, they need to finish the initial series of vaccines, and then receive a booster one year later. This final booster will help to stimulate the memory cells of the immune system, which can then produce large numbers of antibodies if they encounter that particular pathogen again.
As their immune systems mature, animals also develop “cell-mediated immunity,” which is part of the immune system that relies on specific cells and chemicals to attack invaders as they enter the body. Cell-mediated immunity provides the best protection against certain pathogens such as feline leukemia virus and fungal infections. In young animals, vaccines can help provide additional protection until this part of the immune system matures.
Why Do We Continue to Vaccinate Adult Animals?
Some vaccines or infections do produce lifelong immunity. And some infections target young animals with immature immune systems, while older animals will be more resistant to infection (feline leukemia virus is a good example of this.) However, vaccines produce different levels and durations of immunity in individual animals. Nutritional status, concurrent illness, variations in the immune system, and improper vaccine handling can all interfere with an individual’s response to a vaccine. With life-threatening diseases, most of us prefer to err on the side of caution, so we give vaccines regularly, based on average durations of immunity.
Antibody titers can be helpful in determining exposure to infections or vaccines, and a high antibody titer certainly suggests a good immunity, but it doesn’t guarantee it. Furthermore, many pets with low titers are protected by cell-mediated immunity or by memory cells that can produce large numbers of antibodies in the case of actual exposure. For legal purposes and for travel to some areas, rabies antibody titers are used to determine whether an animal has been effectively vaccinated. Rabies titers should not be used as an alternative to vaccination, however, unless the individual animal has had a life-threatening reaction to this vaccine, or has a health problem that could be worsened by vaccination.
What Are the Risks of Vaccination?
Vaccine associated reactions are uncommon, especially when high quality vaccines are used. The most common reaction is mild discomfort and lethargy, which usually resolves in a day or two. Occasionally an animal will develop a small lump at the vaccination site; this usually resolves on its own within 6 weeks. Sometimes a reaction may present as swelling of the face and muzzle, hives, and itchiness.
Life-threatening reactions are thankfully rare. Anaphylactic reactions usually occur within 1-2 hours of vaccination. The animal may vomit, have diarrhea, and collapse acutely. Body temperature and blood pressure drop dangerously. If not treated quickly, these reactions may result in death. If a pet has a severe reaction to a vaccine, future vaccination may not be recommended, or pre-treatment with antihistamines and corticosteroids may be needed prior to vaccination.
In cats, we also worry about the phenomenon of vaccine-associated tumors developing later in life. These are thought to be caused by inflammatory reactions to compounds in the vaccines known as adjuvants. We use non-adjuvanted rabies and leukemia vaccines in cats in order to minimize this risk.
What Are the Health Benefits of Vaccinations?
Although they have sometimes been vilified, vaccines are designed to protect animals and populations of animals, at very low risk to each individual. Since we have started vaccinating young animals routinely for canine and feline distemper, we rarely see these diseases. Even in cases where vaccination cannot completely prevent disease, it will often reduce the severity. Vaccination programs also protect humans, reducing risks of zoonotic diseases such as rabies and leptospirosis. If you have a young puppy or kitten, vaccines are an extremely important part of basic health care, in addition to good nutrition, behavior training, and parasite prevention. If you have an adult pet, you should discuss vaccinations with your veterinarian, and plan a vaccination program that is appropriate for your pet’s life-style and health status.