Categories: vaccinations

How do cat vaccinations work?

In a sentence, cat vaccinations stimulate the making of antibodies specific to a certain germ and these antibodies are part of the immune system which destroys the germ.

Some terms used

I think we need to look at some the words used in describing how cat vaccinations work.

“Pathogens” is a biological term which means anything that can cause a disease. In layman’s language it’s a germ.

“Antibodies” are protein substances produced by the reticuloendothelial system (part of the immune system). This is made up of white blood cells, lymph nodes, and special cells in the bone marrow, liver, lungs and spleen.

“Antigens” are molecules which induce (stimulate) a response by the immune system in the cat (in this instance).

These terms apply equally to cats and humans.

Natural exposure

Antibodies can be produced in the cat’s body by way of natural exposure to a disease or by a vaccine. When a cat becomes ill because of the presence of a germ inside her body the cat’s immune system makes antibodies which fights the particular pathogen (germ) which is causing the illness.

The antibodies created are very specific by which I mean that they only destroy the type of germ which stimulated their production. The antibodies kill the germ and they remain in the body after the germ has been killed and prevent reinfection. At this point the cat has become immune to that particular infection. The cat continues to make antibodies after the disease has gone away. If and when the cat is re-exposed to that particular pathogen her immune system makes more antibodies.

The length of time that the natural immunity works depends upon the type of germ and the individual cat. Sometimes after a natural exposure to a pathogen immunity can last for the cat’s life.


Vaccinations work in the same way as natural exposure to pathogens. Rather than waiting for a cat to be infected by a pathogen, a veterinarian administers “heat-killed pathogens”. Alternatively the vaccine contains antigens which have been treated to make them less infectious. The heat-killed pathogens are not able to cause disease. These stimulate the cat’s immune system as in natural exposure. The vaccine therefore stimulates the creation of antibodies specific to that particular pathogen in the vaccine.

Unlike when exposure to disease is natural the length of protection from a vaccine may be limited. Therefore booster vaccines are recommended. The frequency of booster vaccinations depends on the antigen, the cats immune response, the type of vaccination and the number of exposure to the pathogens.


In layman’s terms, therefore, cat vaccinations work by artificially exposing the cat to a controlled, very low-level version of the disease that the vaccine is intended to protect the cat from. The cat creates antibodies from her own immune system which then allows the cat to protect herself naturally from infection to that specific disease.


There has been controversy of booster vaccinations. Too many have been given for commercial purposes. Vaccinations carry a health risk to the cat. There are rules on administering vaccines to minimise these risks.

I welcome the input of anyone with personal experience and qualifications which allow them to add to the page or amend it.

My thanks to Cat Owner’s Home Veterinary Handbook for holding my hand through this.

Please comment here using either Facebook or WordPress (when available).
Michael Broad

Hi, I'm a 71-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I have a girlfriend, Michelle. I love nature, cats and all animals. I am concerned about their welfare.

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