Feline Vaccinations

by Dr. Fern Slack, UCVC Medical Director and Feline-Exclusive Veterinarian

Feline Vaccination: What You Need To Know When Vaccinating Your Cat (Part 1)

The goal of feline vaccination is to create immunity in response to infectious disease risk. A rational decision regarding vaccination, to the surprise of nearly all cat parents, requires an understanding of:

How immunity works;
The risks associated with the infectious diseases in question;
The risks, benefits, and costs associated with vaccinations;
The options available to minimize those risks, and the costs of those options;
The potential costs of treating infectious diseases in an unprotected cat; and
The potential costs of dealing with diseases (both acute and chronic) caused or worsened by vaccination.

As a caring cat parent, your best resource is a “decision toolbox,” a mental library of knowledge about each of these points; as well as a clear understanding of your own risk tolerance and budgetary limitations. This is the beginning of a five-part series on feline vaccinations and the information you need to know to make the best decisions for your cat.

Filling your toolbox begins with understanding the fundamental differences between “immunity” and “vaccination.”

“Immunity” versus “Vaccination”

Immunity does NOT necessarily result from feline vaccination.

“Immunity,” the ability of your cat’s immune system to fight off a specific disease, is what we hope results from feline vaccinations. Whether or not immunity does result from vaccination depends on a long list of factors:

The vaccine product itself might be of poor quality.
The vaccine product may have been rendered inactive by exposure to heat during transport.
The vaccine product may be administered incorrectly.
Too much time may have elapsed between vaccines in a series.
The patient may already have sufficient immunity.
The patient may have a compromised ability to respond due to age, maternal antibody, or concurrent health problems.
The virus itself may have mutated.

Immunity does not require vaccination.

It can occur as a result of disease exposure, and often does.

Immunity from feline vaccination can last much longer than a year.

For many cats, immunity from early vaccination, especially for the “Distemper” virus, can last most or all of a lifetime. There is nothing magical about the time on the vaccine label; that’s just how long they tested it for.

Immunity is a spectrum, not a totality.

It is a common misconception that all feline vaccines create total, 100% protection against a disease. This is simply untrue.

Feline vaccines against potentially fatal zoonotic diseases, such as rabies, usually have a very high protection rate, but even rabies vaccines do not generate 100% protection in every recipient.

Many of the feline vaccines we use regularly, such as the Feline Leukemia vaccine, provide, at best, a 60% protection against a strong challenge.

Some feline vaccine products provide little or no demonstrable protection at all for an individual cat, but may help a population (such as a cattery) have a slight statistical drop in disease prevalence.

More immunity is not better – in a way, more immunity is not even a “thing.”

Immunity is more like calling up the reserves than sending in the troops. In a nutshell, here’s how immunity works: your cat gets vaccinated for or exposed to a disease. The lymphocytes look at the disease organism, and some of them learn how to fight it. Those lymphocytes teach others, and the “educated” lymphocytes begin manufacturing antibody. If your cat was exposed, antibodies fight off the invader; if your cat was vaccinated, you get a peak of antibody level in the blood that then tapers off. The cool thing happens at the next exposure. Your cat has just a few lymphocytes left that remember how to make this particular antibody, and they keep a little antibody production running for a first line of defense. Then your cat gets exposed again. That tiny pool of lymphocytes gets an urgent telegram that an attack has begun, and they not only crank up antibody production, but also spread instructions like mad so that other lymphocytes can join in. There is an upper limit to the resting population of educated lymphocytes, to the amount of antibody production that occurs in the absence of a challenge, and to the maximum amount of antibody that can be produced during a challenge. If your cat is at that upper limit, more vaccinations are not going to increase the effective immunity.

You can see that when it comes to feline vaccination, “vaccinating your cat” and “ensuring immunity in your cat” are two very different things, and that knowledge is the first tool you need to make reasonable decisions about vaccinating your cat.

The next item in your decision toolbox should be knowledge of the risks associated with vaccination. We’ll look at that in Part 2 of this series.