I and many US veterinarians vaccinate kitties for rabies when they are at least 12 weeks old (or 3 months old), with the standard interval between 3 to 6 months. The combo includes vaccines for chlamydia, feline rhinotracheitis, panleukopenia and calici virus are administered typically at 8 and 12 weeks. Certainly there is a wide margin for schedules, and I am certain that readers on this list will have their favorites.
Early vaccination may cause some problems for very young kitties, and may not help if maternal antibody is still at protective levels in the neonate. Nursing kitties pick up mother's antibodies while nursing, and also received them via the placenta while in utero. It takes time for this maternal antibody to decay at different rates in the individual. That is why we vaccinate on a schedule: not every dose is completely effective, and only by a booster system can we be reasonably assured of vaccine protection.
Any harm from vaccination may be fever/pain at vaccine site/malaise/inappetence/very remote chance of fibrosarcoma/infection. There may be other complications, but they are extremely unlikely if good protocol is followed.
Every medical procedure is at risk, we must always weigh benefit versus harm in a realistic framework.
One other point, modern vaccines are subunit type vaccines or killed types, therefore, they are incapable of causing the infectious diseases they were meant to prevent.
Dr. Van Lienden
Dr. Raymond Van Lienden DVM
The Animal Clinic of Clifton
12702 Chapel Road, Clifton
Virginia, U.S.A. 20124