Cats, even indoor cats, need to be vaccinated to protect them against common cat diseases such as feline distemper (FPV), feline calicivirus (FCV), chlamydia, and feline rhinotracheitis. Vaccines work by stimulating the body’s defense system to produce antibodies for fighting pathogens in the environment. Vaccines are typically administered through injection. 

For vaccines to work effectively, they should be given at the right time. At birth, a kitten’s immune system is considered "naive" as it has not been exposed to any kind of virus or pathogen yet. As she grows, she gains some immunity from those viruses through her mother’s milk. This maternal immunity is not permanent. At age 5-6 weeks, the immunity begins to wane. By age 20 weeks, the antibodies from the mother are completely gone. The purpose of vaccination is to prepare your pet’s immune system with antibodies against invasion of pathogens. FPV, FCV, CP, and FHV should be administered to kittens at age 7 - 9 weeks. At 12-13 weeks, they should be given FIV and FLV shots. AT 13-14 weeks, bring them back to the vet for rabies shots. A single injection of each vaccine at the right time is often enough to give your pet a long-lasting immunity against many cat diseases. 

Some vaccines provide protection for one year only so cat to the vet once a year for re-vaccination. Other vaccines have 3-year duration and others like panoleukopenia and calicivirus last several years. The booster shots are designed to maintain your pet’s immunity at protective levels.