An animal’s eyes have the power to speak a great language.
~ Martin Buber

FAQs About Pet Vaccinations

How do vaccinations work?

Vaccines work by stimulating the body’s defense mechanisms or immune system to produce antibodies to microorganisms such as a virus, bacteria, or otherinfectious organisms. The animal’s immune system is then prepared to react to a future infection with that microorganism(s). The reaction will either prevent infection or lessen the severity of infection and help promote rapid recovery.

What is immunity?

Immunity is a complex series of defense mechanisms by which an animal is able to resist an infection or, minimally, resist disease and the harmful consequences of the infection. Immunity is not absolute. Immunity can sometimes be overcome when there is an overwhelming exposure to a high dose of a virulent or particularly harmful strain of the microorganism or when the animal is unduly stressed or its immune system is otherwise depressed, known as immunosuppression, by other infections.

two Chihuahuas

Beagle getting vaccinated

What is maternal immunity?

Newborn animals have not yet had a chance to make their own immunity, so they need protection against infections present in their environment. They receive this immunity from their mother. Maternal immunity is only temporary. It declines steadily over the first few weeks of life and is largely gone by 12 weeks. The rate of decline is variable depending on many factors.

Why is more than one dose of vaccine given?

Without complicated testing, it is impossible to know when a pup or kitten has lost the immunity it gets from its mother, called maternal immunity. An early decline in a pet’s maternal antibody can leave it susceptible to infection at a very young age, but a strong maternal immunity can actually interfere with early vaccination. The first vaccination is a “priming” dose, and subsequent doses are needed to boost the response to a higher, longer-lasting level of immunity.

Some causes for “vaccine failure” include:

  • Ineffective vaccine—Vaccines made by FDA–licensed manufacturers are potent at the time they leave the factory; however, several things may happen to inactivate them. The most common cause of vaccine inactivation is that the vaccine has been allowed to become too warm. Temperature is critical in maintaining potency. If the vaccine becomes too warm during shipment to the distributor or while being stored at the distributor, it is inactivated. This is a common problem associated with vaccines purchased by Internet, mail, or from feed stores. The buyer has no way to determine whether the vaccines were handled properly during shipment to non–veterinary suppliers. Veterinarians routinely refuse to accept shipments of vaccine if the vaccine is warm or has been delayed.
  • Interference due to maternal antibodies—A well–vaccinated female will confer antibodies to the diseases she has been vaccinated against to her puppies or kittens. Such antibodies protect the pet against those diseases for the first several weeks after birth, the most critical period of its life. However, during this same period, the maternally derived antibodies can block the effects of vaccination of the pup or kitten. This blocking effect decreases as the maternal antibody disappears over several weeks. A point in time is reached, between 6 weeks and 18 weeks of age, when vaccination can be successfully given. Unfortunately, this point varies between pups and kittens. This is the reason that vaccinations are given two weeks apart in the puppy vaccination program, starting at 6 weeks and finishing at 18 weeks of age.
  • Incomplete immune response/immune suppression—There is variation between dogs in their immune system. Some respond less well to vaccination, so immunity may be incomplete or shorter lived than normal. Certain breeds and genetic lines have a tendency for such problems. Certain infections may cause a suppression of the immune system so that an otherwise well-vaccinated pet becomes susceptible to infection and disease if exposed.
  • Declining immunity—Without booster vaccinations, immunity to the specific organism declines over time. There may come a time when there is a particularly heavy dose of the organism from the environment and declining immunity may be insufficient and overwhelmed, resulting in disease.
  • New strains of organism—Some infectious agents exist in different strains or new strains evolve that are not directly covered by the vaccines given. There may be some “cross-protection,” but it may not be complete.