The answer depends in part upon the vaccine. Recent research suggests that panleukopenia, rhinotracheitis, and calicivirus vaccines provide adequate protection for several years, so that many veterinarians are now recommending that this vaccine be boosted no more than once every three years. Unfortunately, far less is known about the duration of protection provided by other vaccines. Until that information is known, annual vaccination with those products when their administration is necessary is a good idea. Unfortunately, a perfect, risk-free vaccine does not exist.
Vaccines are indispensable in fighting feline infectious disease.
But as with any medical procedure, there is a small chance that reactions may develop as a result of vaccination. To maximize the benefits of vaccination while minimizing the risks, it is important to vaccinate only against infectious agents to which your cat has a realistic risk of exposure, infection, and subsequent development of disease. Also, make sure to inform your veterinarian of any problems your cat is currently experiencing, medications your cat is receiving, or vaccine reactions experienced in the past before your cat is vaccinated again. The following reactions are fairly common and usually start within hours to several days after vaccination. They typically last no more than a few days.