Occasionally, a dog or cat may have an allergic response to a vaccination. This seems more prevalent in dachshunds. The reactions are sometimes disconcerting, and may require treatment, but are rarely fatal. Pets who have had serious reactions may be better off without vaccinations. But this is a choice of the lesser of two evils.
Rabies is now a rare disease in dogs and cats in most of the United States.
Most of us veterinarians can remember when the parvovirus epidemic first swept across the country and killed many young puppies as well as healthy adult dogs. Fifteen years ago feline leukemia was a common cause of death in cats. At about that time we started vaccinating routinely for feline leukemia. We now rarely see the disease or a positive blood test. There is no doubt that the number of animals that died each year from these diseases before modern vaccination programs is many times greater than the number of cases of vaccine induced fibrosarcomas or other serious vaccination reactions.