What shots are absolutely necessary for my 9-month-old cat? She is in the house all the time. Our last Himalayan almost died from its shots.

Watertown, SD

Vaccines are a perennially controversial subject in veterinary (and human) medicine. There is no doubt that undervaccination is dangerous. Unvaccinated cats and kittens frequently die needlessly from diseases such as panleukopenia or feline leukemia. In cats especially, there is almost no doubt that over-vaccination is dangerous as well — some vaccines have been linked to cancers in cats (more on that below). The goal when vaccinating cats is to strike a balance between these two dangers. Sadly, since the dangers aren’t measurable, and since every individual has unique needs, a perfect balance is a tough target. However, a reasonable balance isn’t that hard to achieve.

Set a schedule with your vet to discuss what shots your indoor cat may need.

The most important thing to remember when vaccinating your pet is that every pet has unique needs. These needs are based upon the animal’s lifestyle, geographic location, and immune system function. Immune system function is difficult to quantify (although blood tests called titers offer some insight into it). Lifestyle and geographic location, however, are pretty straightforward. The main lifestyle consideration for cats is whether they go outside. The main geographic consideration for cats is the prevalence of rabies and the existence (or absence) of laws that mandate feline rabies vaccinations.

There are three commonly used (so-called core) vaccines in cats. The first, and least controversial vaccine protects against panleukopenia (a deadly virus that is related to canine parvovirus), usually in combination with a vaccine against certain upper respiratory diseases (the combination vaccine is usually referred to as an FVRCP). This vaccine is recommended in all cats, regardless of their lifestyles or where they live. Although no definitively determined schedule has been developed for this vaccine, most experts have come to a consensus. They generally recommend a series of two or three injections as a kitten (depending upon the kitten’s age), a booster one year later, and then subsequent boosters no more often than every three years.

The second core feline vaccine protects against feline leukemia virus, or FeLV. This virus is a threat only to outdoor cats, or to cats who may come in contact with outdoor cats. The initial kitten series consists of two injections. The vaccine is then boostered one year later, and then every 1 – 3 years depending upon the type of vaccine that is used. The FeLV vaccine has been linked to tumors (called sarcomas) at the site of injection. Initially these tumors were thought to be linked to a product called adjuvant in the vaccine, but I have yet to see conclusive evidence that adjuvant is the culprit. Owners of indoor cats have two options. They can either forego the vaccine altogether, or, if they are concerned that their cats might escape, they can elect to administer the initial kitten series but no boosters (which, it is thought, will provide limited immunity and limited risk of tumors).

The final core vaccine is the rabies vaccine. Unfortunately, rabies vaccines also have been linked to sarcomas. Indoor cats are at very low risk of rabies. However, rabies has the unpleasant distinction of being the most deadly infectious disease known to cats, dogs, and people. Cat owners who live in an area where rabies is common, or cat owners with small children or other people who desire protection against rabies, may decide to pursue rabies vaccination. Also, rabies vaccines are required by law for cats in some municipalities. Rabies vaccines are generally given at or after 16 weeks of age, then boostered one year later, and then at intervals of one to three years depending upon vaccine type and local law.

Several other vaccines, such as the feline Bordetella vaccine, the FIV/feline AIDS vaccine, and the ringworm vaccine are not generally recommended by experts.

Gloria, if you are absolutely certain that you can keep your cat indoors with no escapes, then I would recommend that she receive the panleukopenia (also known as FVRCP) vaccine but not the leukemia vaccine. You should discuss the prevalence of rabies as well as legal requirements for rabies vaccination with your vet before deciding whether to administer the rabies vaccine.