Vaccinations have saved the lives of millions of cats. Before the days of effective vaccines, cats routinely died from panleukopenia ("feline distemper") and complications of upper respiratory (herpesvirus, calicivirus) infections. Newer vaccines are available to protect against feline leukemia virus infection, feline infectious peritonitis virus and other infections (chlamydia, feline bordetella, ringworm). Current vaccination programs also protect our cats (and us) from the threat of rabies.
Traditional vaccines are administered by injection (shots), but newer vaccines can be administered through the nostrils and have been developed to protect against a variety of infections. Despite the well-known benefits of vaccination, the practice of annual vaccination of mature cats is controversial. Some veterinarians believe that annual revaccination is an important and critical part of preventative health care. Others suggest that there is little scientific information to suggest that annual revaccination of older cats is necessary for some diseases because immunity to many viruses probably persists for the life of the animal.
The major concern about repeated vaccinations in cats is the issue of feline vaccine-associated sarcoma, a cancer that develops in approximately 1 of every 1,000 cats to as few as 1 in every 10,000 cats near the site of vaccination. Certainly routine vaccinations are essential for prevention of infectious diseases in kittens. Of course, some vaccines(rabies) are required by law and must be administered on a regular basis. Kittens receive immunity against infectious disease in the mother's milk; however, this protection begins to disappear in the first few months of life.
To protect kittens during this critical time, a well-researched approach is taken: A series of vaccines is given every 3 to 4 weeks until the chance of contracting an infectious disease is very low. The typical vaccine is a "combination" that protects against feline distemper virus, feline calicivirus, and feline herpesvirus. Rabies vaccines are given between 16 and 26 weeks of age in most states (governed by law). Some cats are also immunized against feline leukemia virus. The usual approach is to test the kitten for feline leukemia at the time of initial vaccination to ensure the cat is not harboring the virus. The use of other vaccinations is on a case-by-case basis. Booster immunizations are given during the first one or two years of "adult" life. Thereafter, the issue becomes cloudier. Don't be surprised if you encounter different views about booster immunizations. There has been insufficient research conducted in this area of long-term protection vs. risk of vaccine-associated sarcoma (tumors).
You should discuss all vaccination programs with your veterinarian.
If the risk of feline leukemia virus exposure is significant (out-of-doors cats), the leukemia virus vaccine sequence should be administered. Other vaccines are given on a case-by-case basis. Some veterinarians use traditional "shots" for vaccination while others use a combination of injections and intra-nasal vaccines. The rabies vaccines should be given as required by local laws.