Dr. Kather's Pet Tips

​Understanding Feline Vaccines

There are three main vaccines that are offered to cats in the United States to help prevent specific feline viral diseases. The vaccines that are considered “core” vaccines include FVRCP and Rabies vaccines. These vaccines are recommended for every cat. A third vaccine, the feline leukemia virus vaccine, is only recommended for young at-risk cats. Understanding what each vaccine protects against and the vaccination protocols for animals less than four months of age helps pet owners make informed decisions on what is needed to protect their cat. 

FVRCP (Feline Viral Rhinotracheitis, Calicivirus and Panleukopenia)

This vaccine is an acronym that represents three different feline viruses, often referred to as a “3-in-1” vaccine.

  1. ​The Feline Viral Rhinotracheitis is another term for the Feline Herpes 1 virus. This is a species-specific virus that causes upper respiratory symptoms in cats including nasal discharge, sneezing and congestion as well as ocular discharge and possible ulcer formations on the cornea (surface of the eye). This virus, like the human rhinotracheitis virus (common cold), is highly contagious in cats and is spread through aerosolized respiratory secretions. Vaccination often only leads to partial immunity in adult cats, however, if exposed to the virus, a fully vaccinated cat is more likely to have a shorter and milder course of illness.
  2. The second virus in this vaccine is the feline Calicivirus. This is another highly contagious upper respiratory virus that affects cats. It can cause similar symptoms to feline herpes virus but is often also associated with ulcerations in the mouth and tongue. Vaccination is very effective at preventing disease in adult cats.
  3. The last virus in this vaccine is the Feline Panleukopenia virus, a highly contagious viral disease of cats caused by the feline parvovirus. Kittens are most severely affected by the virus due to maternal antibody interference with vaccine efficacy. Feline distemper and feline parvo should not be confused with canine distemper or canine parvo— although their names are similar, they are caused by different viruses do not affect people. The feline parvovirus infects and kills cells that are rapidly growing and dividing, such as those in the bone marrow and intestines. Clinical signs are variable and may include lethargy, dehydration, vomiting, diarrhea, or even sudden death.

A vet administers a shot to a kitten


    Kittens less than 4 months of age, which are the most vulnerable to infection, represent the majority of feline population in shelters for most of the year. Because of this, proper vaccination and sanitation protocols are essential to minimize spread of diseases and mortality in this group. Shelter vaccination recommendations include providing the first FVRCP vaccine at 4-5 weeks of age and boosting the vaccine every 2-3 weeks while in the high risk shelter environment. The reason that kittens need frequent boosters is multifactorial and includes (1) interference of maternal-derived antibodies (MDA) that can prevent the kitten from mounting its own immune response, (2) stress, (3) concurrent disease or infection, (4) immunosuppression, and (5) malnutrition.

    Because there is no way to determine when a specific kitten has developed protective antibodies, all kittens are revaccinated every 2-3 weeks until they are 4 months of age. At this age it is known that the largest interference with vaccine-induced immunity, MDA’s, are no longer a factor and immunity is then thought to last for 1 year. Therefore, it is not the number of boosters that determines adequate vaccine-induced immunity but the age of the kitten when a vaccine is administered. Many kittens come into shelters as pre-weans (less than 3 weeks of age) and may receive as many as 4-5 vaccinations by the time they are 4 months of age. An older kitten, however, may only receive 2 vaccinations until it is considered protected.


    Rabies is a viral disease that attacks the brain and spinal cord of all mammalian species, including cats, dogs and humans. It is primarily transmitted through a bite from an infected animal as the virus is shed in high numbers through the saliva. Rabies disease is almost 100% fatal, however, vaccination is extremely effective and in California can be administered as early as 12 weeks of age to dogs and cats. Revaccination is recommended at 1 year and subsequent vaccination every 3 years.

    FeLV (Feline Leukemia Virus)

    Considered a non-core vaccine, the FeLV vaccine is intended for young cats in a high-risk environment. The virus is shed through many bodily secretions and transmission occurs through sustained contact. Thankfully the prevalence of this disease in domestic cats in the United States is very low. Large serosurveys have documented a prevalence of <3 % and recent statistics from our own shelter confirmed an extremely low prevalence among healthy cats and kittens. We tested 2,489 cats and kittens between January of 2015 and January of 2019 and found only 6 FeLV positive cats (0.2%). Vaccination should be considered for cats with access to outdoors, living with a known FeLV positive cat, or m​ulti-cat households in which viral status is unknown. Duration of immunity after the initial vaccine series is thought to be at least 2 years, therefore cats still in at at-risk environment should continue to be vaccinated every 2 years.

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