I recently read Lauren Oster’s Catster article, “Cats and the City: 5 Lessons of Urban Life With Felines.” In an especially amusing paragraph under the heading “‘Indoor-only’ cats become ‘no, seriously, like 100 percent indoors'”, Oster points out the absurdity of vaccinating 100 percent indoor only cats against rabies. Because rabies isn’t exactly endemic in Manhattan, why would any vet recommend rabies vaccines for Oster’s cats?

I’ll take it a step further. Why would any vet recommend any vaccines for indoor-only cats?

As with all matters related to vaccines and cats, the answer isn’t simple at all. In fact, some vets do not recommend regular vaccination for indoor cats. Others do, and for various reasons.

Only one thing about feline vaccinations is without dispute in the veterinary community. There is no doubt that all cats benefit from some degree of vaccination. There is nearly universal consensus that kittens should receive at least one vaccine against feline panleukopenia virus, which is also known as “panleuk,” feline parvovirus, and feline distemper virus. (The nomenclature of the disease is confusing, because canine parvovirus and canine distemper virus are completely different things. In fact, the feline virus is a parvovirus, but for some reason many people refer to it as distemper.) The panleuk vaccine generally is administered in a single syringe in combination with vaccines against calicivirus and rhinotracheitis — the so-called FVRCP. However, panleuk is a horrible killer of kittens, and its component of the vaccine is most important.

After that first vaccine, the consensus falls apart. The overwhelming majority of vets, but not quite all of them, firmly believe that the complete kitten series of FVRCPs is very important. Kittens usually obtain antibodies against panelukopenia when they nurse from their mothers during the first days of life. Those antibodies protect them against the disease for the next couple of months. They also inactivate any vaccine that is administered when they are present in the body. The duration of their presence in the body is variable. Therefore, the overwhelming majority of vets believe that several vaccines should be administered during the first few months of life, in an effort to increase the chances of timing the injections correctly. The few dissenters point out that studies have shown that in perfect circumstances a single panleuk vaccine can provide lifetime immunity for cats.

A very large, but not quite so overwhelming, majority of veterinarians recommends a panleuk shot at one year of age to boost immunity. After that, there is no consensus.

A minority of vets recommend annual administration of FVRCPs for indoor cats because they believe vaccine reminders are the only way to get cats into their offices for what they really need: regular examinations and health checks. In my experience there is little basis for this belief. Responsible cat owners generally are more interested in the health checks than in the vaccines.

Another group of veterinarians, including some highly reputable experts, recommend regular FVRCPs for indoor cats for another, almost paradoxical reason. They point out that indoor cats are less likely to be exposed to diseases in the course of their normal lives. Their immune systems therefore do not receive regular stimulation which might be necessary to retain immunity. Therefore, according to this line of thought, indoor cats might need vaccines more often than outdoor cats so that their immune systems will be competent if they are exposed to a pathogen.

Although this logic makes some sense theoretically, in practice I don’t buy it. In my experience, infectious disease rates are much lower for indoor cats than their counterparts who go outside. However, personal experience is notoriously prone to biases and inaccuracies. I have not yet seen good data to support or refute this theory.

Most vets now recommend reduced FVRCP frequency for all cats, including indoor cats. Several reputable organizations, including many veterinary teaching hospitals and leading veterinary groups , recommend administering FVRCPs every three years. A triennial vaccination schedule now is probably the most commonly recommended one. However, many vets are taking it further, and and recommending FVRCPs less frequently. Many vets recommend five-year schedules, some recommend seven-year schedules, and a minority recommend no vaccinations during adulthood.

This article has covered FVRCPs extensively, but it was the absurdity of vaccinating indoor cats against rabies that triggered the topic. Why would a veterinarian recommend rabies vaccines for indoor cats?

The answer is actually simple. In some cases, we have to.

In many municipalities, rabies vaccine schedules are not driven by science. They are driven by law. Many people, including Oster, live in places where feline rabies vaccines are legally mandated. Vets who don’t recommend following the law risk legal sanction and liability lawsuits.

Who wrote the laws? Not vets. Are the laws scientifically founded? Not in my opinion. To my knowledge, the rate of feline rabies is the same (0 percent) in San Francisco, where feline rabies vaccines are not required, as in New York, where they are.

What can be done about this? If you live in a place where feline rabies vaccines are required by law, you can write to your local lawmakers. But don’t hold your breath. In my experience, it is a fool’s errand to hope that the government will be reasonable.

Read more on cats and health:

• 5 Things I Did Wrong When I Took My Cat to the Vet
• Has Your Cat Ever Given Your Vet a Funny Story?
• 11 Cat Emergencies That Need Immediate Veterinary Attention

Got a question for Dr. Barchas? Ask our vet in the comments below and your topic might be featured in an upcoming column. (Note that if you have an emergency situation, please see your own vet immediately!)