Last week we talked about essential vaccines for cats (rabies, feline viral rhinotracheitis, panleukopenia, and calicivirus) that virtually every cat should receive on a regular basis. Today, let’s touch on the first of the situational vaccines — feline leukemia virus (FELV).

First a bit of background on the disease. Cats primarily come in contact with FELV through bites inflicted by infected cats, but the virus can also be spread through mutual grooming or sharing food bowls and litter boxes, and pregnant females can pass the disease on to their offspring. Some individuals can fight off the virus, but once infection is established, the consequences are dire. FELV attacks and weakens the immune system. Early in the course of the diseases, cats often do not appear to be sick. But as immune function declines, they become susceptible to life-threatening infections, immune-mediated disorders, and certain types of cancer. Some cats with FELV can enjoy long, relatively healthy lives, but most eventually succumb to the disease. Treatment is limited to symptomatic and supportive care.

Given that FELV infections are so serious, you might be wondering why the vaccination is considered situational rather than essential. The reasoning is based on the fact that the risk of infection can be virtually eliminated by keeping cats indoors-only and screening new feline additions to the household. Also, FELV vaccines have been associated with a higher than average risk of injection site sarcomas, an aggressive type of cancer. New vaccine manufacturing techniques have greatly reduced but, unfortunately, not eliminated that risk. These recombinant FELV vaccines are now the only ones I will use.

Now, let me temper the definition of “situational” in the case of FELV by saying that I do consider the vaccine essential for kittens. I recommend that all of my pediatric feline patients receive two doses of a recombinant FELV vaccine 3-4 weeks apart (usually starting around eight weeks of age). This applies regardless of whether or not an owner plans on keeping his or her cat indoors. I make this recommendation because young cats are at highest risk for becoming infected with FELV (adults have greater innate immunity), and it can be difficult to establish a cat’s lifestyle until he or she is grown. (Some owners find it next to impossible to prevent a cat from going outside as he or she grows and becomes more determined and crafty.)

After these first two “kitten” vaccines, I reassess the situation at every annual check-up. If the cat has successfully been kept indoors and that remains the plan for the continuing year, I do not recommend vaccination against FELV. But, if the cat is at high risk for the disease (e.g., going outside or living with a FELV positive housemate) a booster should be given.

Currently, all FELV vaccines are labeled for annual (rather than every three year) revaccination intervals, and there are no definitive studies that show a longer duration of immunity. That said, as cats get older, I do become increasingly more comfortable lengthening the time between FELV vaccines and eventually discontinuing them altogether as long as owners are aware of the potential pros and cons of this approach and the cat’s risk of infection is not terribly high.

Dr. Jennifer Coates

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