A Dogster reader recently asked about vaccine protocols for six-month-old puppies. The Internet is rife with recommendations for 2-month-old puppies, but devoid of answers for older ones.

I answered her question, but it occurred to me that puppy and dog adopters aren’t alone. Plenty of people rescue or adopt older kittens, or full-grown cats, from uncertain backgrounds. The vaccination history of these feline companions may be questionable, or it may be clear that no vaccines have been administered. Which vaccines are appropriate?

Vaccines in cats are divided into two groups. Core vaccines are the ones that are critically important. Optional, or noncore, vaccines are available as well. but are not recommended for most cats.

There is only one universal core vaccine for cats: the FVRCP, which protects against feline viral rhinotracheitis (FVR), calicivirus (C), and, most important, panleukopenia (P). Panleukopenia, confusingly, is also known as feline distemper and feline parvovirus, and is related to the canine parvovirus (in fact, it is thought to be a descendant of panleukopenia that jumped from cats to dogs, although it is not related to the canine distemper virus.) Panleukopenia is a devastating, ultra-contagious disease that kills a huge proportion of cats and especially kittens. Although the FVR and C are important, the most critical part of the vaccine is the P.

Previously unvaccinated kittens and cats older than 4 months should receive two FVRCPs separated by two to four weeks, with a booster one year later and subsequent boosters every three years at most. Depending upon lifestyle and age, many cats do well receiving FVRCPs less often than every three years in the long term.

Rabies vaccines are considered core for cats who live in areas where they are legally required, in order to protect humans from the most deadly infectious disease on Earth (although they do also protect cats). If you live in an area where feline rabies vaccination is optional, you should consider two things: First, vaccinating the cat may help to protect people in the household from the disease (and also protect the cat from rabies testing — which requires euthanasia — if someone is bitten). Second, rabies vaccines have been linked to sarcomas in cats. Newer, so-called non-adjuvanted vaccines claim to reduce the risk of cancer, but I have yet to see conclusive evidence that they are truly safer. There is only one way to decide: Have a comprehensive discussion with your vet.

If you decide to vaccinate your cat or older kitten against rabies, here is the schedule: A single vaccine, followed by a booster in one year. Subsequent vaccines should be administered every one or three years as required by law or recommended by the manufacturer.

For cats with outdoor access, the feline leukemia vaccine is considered core, but these, like rabies vaccines, have been linked to cancers in cats. Discuss the risks with your veterinarian first. Leukemia vaccines generally are not recommended for indoor cats.

The leukemia schedule recommended for cats and older kittens is a series of two injections separated by two to four weeks, with a booster at one year, and then boosters every one to three years (depending upon the type of vaccine used). Be aware that leukemia rarely strikes older cats — therefore, I usually recommend backing off of leukemia vaccines after age five.

There are several optional vaccines for cats, including vaccines against ringworm, coronavirus (FIP), and FIV/feline AIDS. Although there are occasional exceptions, these vaccines are not appropriate for most cats and kittens.

Since some feline vaccines have the potential to cause harm, good communication with your vet is critical. Always talk to your vet about the risks and benefits of any vaccine that your cat might receive.

Finally, don’t forget that unvaccinated cats and kittens usually haven’t been dewormed. Some feline worms can cause serious disease in people (as well as in cats). Be sure to discuss worms with the vet at the same time as you discuss vaccines.

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