Why We Vaccinate (Even Indoor Cats)

As a feline practitioner in New York City, most of my patients live their lives exclusively indoors. Many times during an office visit, when I tell my clients that their cat is due (or overdue) for vaccines, I get asked whether their cat really needs the vaccines. “He’s totally indoors and doesn’t come into contact with any other cats” is something I hear almost every day. Indoor cats DO still need their vaccines. In this blog post, I hope to remind all of my readers (and clients) on the importance of vaccination.

Vaccines have been an integral part of preventive health care programs for several decades. No other medical development has been as successful as vaccination in controlling deadly diseases in companion animals. Vaccination, however, should not be considered a totally benign procedure. In 1991, veterinarians began to notice a higher than expected number of sarcomas, a type of cancer, occurring on cats’ bodies in places where vaccines were often injected. Further studies confirmed an association between vaccine administration and sarcoma development. While the incidence of these sarcomas was very low, their occurrence was devastating, with many cats dying from these tumors.

Vaccination is a medical procedure, and the decision to vaccinate is made based on the risks and benefits for each individual cat. To not vaccinate our pets is not an option. The goal is to devise a reasonable strategy for vaccination that maximizes our ability to prevent infectious disease while minimizing the occurrence of adverse events associated with vaccination.

Vaccinations can be divided into two broad categories: core vaccines – those recommended for all cats, and non-core vaccines – those that may or may not be necessary, depending on the individual cat’s lifestyle and circumstances. Currently, vaccines against panleukopenia, herpesvirus, calicivirus, and rabies fall into the core vaccine category. The most commonly used vaccine against panleukopenia, herpesvirus and calicivirus is a multivalent vaccine: it contains viral antigens for several diseases together in the same dose, and is commonly abbreviated as the “FVRCP” vaccine. [For those of you who’ve always wondered exactly what FVRCP stands for, it’s “Feline Viral Rhinotracheitis, Calicivirus, Panleukopenia”. Feline viral rhinotracheitis is fancy way to describe the respiratory infection caused by the herpes virus. Panleukopenia is the illness caused by the panleukopenia virus. Panleukopenia is often (incorrectly) referred to as “distemper”. Confusing.]  The rabies vaccine is usually a monovalent vaccine. It contains viral antigens for one virus: the rabies virus.
Vaccines against feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), feline infectious peritonitis (FIP), ringworm (a skin fungus), Chlamydophila (a respiratory pathogen, formerly called Chlamydia), and Bordetella (another respiratory pathogen), are considered to be non-core. Some of the non-core vaccines have questionable efficacy and are not generally recommended.

Kittens are the main target population for vaccination, because they are more susceptible to infection than adult cats, and they tend to develop more severe disease compared to adults. The currently recommended vaccination protocol for kittens is as follows:

The kitten vaccination series should begin at 6 to 8 weeks of age. Kittens should initially receive the FVRCP vaccine, with additional boosters given every 3 – 4 weeks until 16 weeks of age. Kittens older than 12 weeks of age should receive an initial FVRCP vaccine, followed by one additional FVRCP booster 3 – 4 weeks later.

Kittens should receive a rabies vaccine at 12 – 16 weeks of age.

The FeLV vaccine is a non-core vaccine in adults, however, the American Association of Feline Practitioners and the Academy of Feline Medicine feel that all kittens should be vaccinated against FeLV, because kittens are especially susceptible to FeLV, and the lifestyles of kittens often change after adoption, increasing their risk for FeLV exposure. A booster vaccine should be given one year later in cats that remain at risk for exposure to FeLV. I personally have mixed feelings about this recommendation, and I usually do not vaccinate kittens for FeLV because in my practice, the lifestyle of kittens does not change after adoption. My clients keep their kittens indoors.

One year after the last pediatric vaccination, an FVRCP vaccine and a rabies vaccine should again be administered.

The vaccination protocol for adult cats is a little different. Cats older than 16 weeks of age that have never been vaccinated against panleukopenia, herpes virus, and calici virus should receive 2 doses of vaccine, three to four weeks apart. A single booster against panleukopenia, herpesvirus, and calicivirus is given one year after the last dose of the pediatric series, and then every 3 years thereafter.


How often the rabies vaccine should be given depends on the vaccine. Some are labeled for annual revaccination. Others are to be given every three years. In my practice, we use a brand of vaccine that needs to be given annually. I’ve been asked why I don’t use a three-year vaccine. The reason is safety. The particular vaccine brand I use is very safe and very effective. It does not contain substances that some people have linked to vaccine-induced sarcomas. I’ve heard that the company that makes this vaccine is in the process of proving that their one-year vaccine actually confers immunity for 3 years, but until they do, I am legally bound to give the vaccine annually. The rabies vaccine is required by law.

The FeLV vaccine is given annually in cats determined to have continued risk of exposure.

Healthy older cats, and those with chronic but stable conditions should be vaccinated in the same fashion as if they were younger adults. Sick cats, however, whether kitten or adult, should not be vaccinated until they have recovered from their illness.

So, what exactly are we vaccinating against? Let me give you a brief summary, and then my own personal opinion as to why these vaccines are important. Let’s start with the “FVR” part of the FVRCP vaccine: the herpesvirus.

Feline herpesvirus is a major cause of upper respiratory disease in cats. Herpesvirus infections are very contagious between cats. Most cats become exposed to the herpesvirus at some time in their lives, and the majority of exposed cats become infected. Cats typically develop a mild upper respiratory infection – sneezing, conjunctivitis (“pink eye”), runny eyes, nasal discharge – which often resolves on its own. In some cats, the virus induces severe upper respiratory disease, and a few of these cats may develop persistent upper respiratory symptoms for years. The herpes virus can also cause a variety of eye disorders, and may cause skin disease as well. Cats of all ages are susceptible, however, kittens appear to be affected more severely than adults. A presumptive diagnosis is made based on evaluation of the cat’s history and clinical signs.
After a cat recovers from the initial infection, the virus remains in the body as a latent infection. The dormant virus can be reactivated during times of stress, crowding and concurrent illness, resulting in a recurrence of clinical signs. During these recurrences, infected cats shed the virus profusely in their eye, nasal, and oral secretions, increasing the risk of infecting other cats. There are currently no drugs that eliminate herpesvirus from the body.

The feline calici virus (the “C” in the FVRCP vaccine) is an important cause of upper respiratory and oral disease in cats. Respiratory signs caused by calicivirus (sneezing, ocular discharge, nasal discharge) tend to be milder than those caused by the herpesvirus, however, calici virus may cause ulcers on the tongue of cats and kittens. The virus is mainly transmitted by direct cat-to-cat contact, however, indirect transmission via contamination of the environment or through contaminated objects is also possible. Acutely infected cats will shed the virus in oral, ocular, and nasal secretions for two or three weeks, although some cats become chronic carriers, and will shed the virus persistently for months or even years. Cats of any age are susceptible, although kittens are most susceptible. Cats housed in groups, such as in boarding catteries, shelters, and breeding colonies, are at increased risk for contracting calicivirus.

A more serious, systemic form of calici virus infection caused by a very virulent strain of calicvirus (VS-FCV) has been reported in recent years. Disease caused by VS-FCV tends to be more severe and may be fatal. Fortunately, this hasn’t been a problem here in New York City.

Panleukopenia (the “P” in the FVRCP vaccine) is a highly contagious viral disease caused by the feline panleukopenia virus (FPV). Cats infected with the virus often show signs of lethargy, poor appetite, fever, vomiting, and severe diarrhea. The word panleukopenia means “a decrease in white blood cells”, and that is what is seen on the bloodwork of affected cats. In young cats, the disease is often fatal. Queens, if infected during pregnancy, may give birth to kittens with a condition called cerebellar hypoplasia, a neurologic disorder that causes severe incoordination. The virus is spread mainly through contact with feces, however, the virus is very stable in the environment and can be spread via contaminated food bowls, water bowls, litter boxes, and health care workers. Treatment consists mainly of supportive care – hospitalization, fluid therapy, antibiotics, and nutritional support. With aggressive care, some cats survive the infection, however, most succumb to the virus.


So, let’s answer the all-important question of why your totally indoor cat needs to be vaccinated.

The rabies vaccine is required by law. The odds of your cat acquiring rabies is extremely small. Almost zero. However, if your cat was to bite someone, and you didn’t have proof that your cat was vaccinated against rabies, your legal nightmare begins. The only way to prove whether a cat has rabies is to euthanize it, remove its brain, and examine it under a microscope. If your cat was to bite someone, and your cat was current on his rabies vaccine, legally, if the person filed a complaint against you, your cat would have to be quarantined at a veterinary facility for ten days. If no signs of rabies developed after ten days, then your cat doesn’t have rabies. If, however, your cat was not current on his vaccine, and you refused to euthanize your cat and have its brain examined to prove that it did not have rabies, then you would be legally required to quarantine your cat at a veterinary facility for six months (at YOUR own expense). If no signs of rabies were present after six months, then your cat does not have rabies. You would also be legally responsible for the cost of the bite-victim’s (very expensive) post-exposure rabies treatment.
Play it safe. Keep your cat’s rabies vaccine status up to date.

Regarding the FVRCP vaccine: if your cat doesn’t contract panleukopenia during kittenhood and was vaccinated properly, the odds of getting panleukopenia as an adult is practically zero. The calicivirus, while a nuisance, isn’t much of a pathogen in cats. The real reason why we want to keep cats current on their FVRCP vaccine status is that darn herpesvirus. The herpesvirus is responsible for a lot of misery in cats, not only by causing respiratory infections, but by causing a variety of eye problems in cats. The FVRCP vaccine is not designed to prevent infection. Most cats have been exposed to the herpesvirus as kittens, and once you’re infected with a herpesvirus, you’re infected forever. After infection, the herpesvirus stays dormant in the body, usually causing no problems. Every now and then, when a cat gets stressed or sick or immunosuppressed, the herpesvirus can re-emerge from dormancy. Cats who are well-vaccinated usually handle this just fine. The circulating antibodies against the virus will attack the herpes virus and keep things in check. Cats may get a mild head cold, usually nothing serious. Cats who are poorly vaccinated, however, may develop a whopping head cold and/or a variety of eye problems. So, it behooves us to keep our cats current on their FVRCP vaccines. It doesn’t matter that the cat is totally indoors. Cats are not picking up the herpes virus from other cats. The virus is in the body already. The vaccine helps keep it in check, preventing severe clinical signs from occurring if the virus happens to re-emerge from dormancy. That’s the main reason why we continue to vaccinate indoor cats against FVRCP.

Vaccines against infectious diseases have done much to reduce sickness and death in companion animals, and vaccination is the cornerstone of preventive veterinary medicine. As with any medical procedure or decision, the advantages must be balance against the risks, and you and your veterinarian should discuss all of the options now available to determine the best vaccine protocol for your cat.