Vaccinations and Your Pet

Your pet’s immune system functions to protect their body from pathogens such as bacteria, viruses and other microorganisms that can cause disease.

These pathogens are composed of and produce certain proteins known as antigens, and the immune system responds to antigens by producing antibodies that bind to and inactivate antigens to help prevent infection.

There are many medications and products that are used in veterinary medicine to affect the immune system in various beneficial ways, and vaccines are one of the most well-known of these products. Vaccines are a form of specific immunotherapy which involves administering a specific antigen (either a gene or protein fragment from a pathogen or one of the proteins that a pathogen produces during infection) to cause a very specific and controlled immune response. As a result, vaccination can induce a similar immune response to a ‘real infection’ but without the systemic signs of illness, and results in effective and often specific long-term immunity. Adjuvants are sometimes added to a vaccine to increase its effectiveness. Adjuvants are a form of nonspecific immunotherapy, which causes the immune system to produce proteins that strengthen the immune response.

Vaccinations need to be administered on a specific schedule in order to stimulate a significant immune response. When puppies and kittens are nursing, they receive protective antibodies from their mothers that interfere with vaccine-derived immune responses. These maternal antibodies are typically broken down by around 16 weeks of age, so vaccinations are administered every 3-4 weeks until the animal is 16 weeks old in order to ensure an adequate immune response has been established. The schedule for re-vaccination depends on the specific vaccine, but typically vaccines are ‘boosted’ once yearly to once every three years to ensure the individual remains protected. A ‘booster’ is a vaccine that is given to stimulate an immune response again, resulting in a renewed immune response which increases protection.

Deciding When to Vaccinate

Vaccinations are highly effective in controlling infectious diseases when they are properly administered to at-risk individuals. There are several criteria used to determine whether or not a given vaccine should be used in your pet. In all cases, the risk associated with the disease must outweigh the risk associated with vaccination.

• EFFICACY: The vaccine should be effective against the primary pathogen(s) responsible for a given disease or syndrome. For example, Canine Infectious Tracheobronchitis (a.k.a. Kennel Cough) can be caused by multiple different pathogens but we typically only vaccinate against Bordetella Bronchiseptica, canine parainfluenza virus and canine adenovirus type-2, because these are the most common causes of kennel cough and usually cause the most severe clinical signs.
• EXPOSURE: Your pet should have a significant risk of being exposed to the disease being vaccinated against. Using the above example, if your dog attends training classes or doggy daycare where they are frequently in contact with other dogs, their risk of contracting kennel cough is high, and they should be vaccinated. In contrast, a dog that never comes in contact with other dogs has a low risk of exposure, and vaccination against kennel cough may not be necessary.
• PROTECTION: The vaccine should result in rapid onset of a strong and prolonged immunity in vaccinated animals.
• SAFETY: The vaccine should not cause adverse effects. The risks of vaccination must not exceed those caused by the disease itself.
• SCREENING: The vaccine should – ideally, but is not always the case – stimulate an immune response distinguishable from those due to natural infection. This is important to be able to tell the difference between an infected individual and a vaccinated individual.

I hope this blog post has been informative and has helped explain the decision-making process around vaccinations and your pet! I will be writing two follow-up posts next month about the specific types of vaccines administered to dogs and cats in Atlantic Canada.

Written by: Dr. Brittni Milligan