Life is not risk-free. We shouldn’t stop doing beneficial things just because of potential (and rare) side-effects, particularly when the benefits in most cases far outweigh the risks.
A recent article in the Cleveland Examiner discussed feline distemper (panleukopenia) vaccination. The author related the story of a cat that apparently had a "bad" (undescribed) reaction to the vaccine, which is certainly possible. Adverse reactions to vaccines are rare, but they certainly can (and do) occur. It’s important that we don’t react excessively to these highly unfortunate reactions, and end up in a situation where more animals get sick and die from the disease because people get scared of vaccinating against it. (The increasing rates of measles in people in some areas, including serious outcomes, following ill-informed paranoia of an association between vaccination and autism is a great human example of that).
The author goes on to state:
"What should you do to guard your cat against feline distemper? Ask a holistic practitioner for nosodes instead of a vaccine serum." But there is no evidence whatsover that nosodes have any effect. A cat "vaccinated" with a nosode is an unvaccinated cat.
"The diluted formula is safe—it contains no live pathogens– and effective." It’s probably safe, but in no way effective.
"A cat who doesn’t mingle with other animals probably doesn’t need a vaccine against viruses." Bad advice. You’d be amazed by the number of ‘indoor cats’ that are taken to vet clinics after being hit by a car, getting in a fight with a stray cat, or similar non-indoor encounters. Close contact with strays can also occur through screen doors and windows. Then there’s the issue of rabies exposure from bats in houses. Altogether, avoiding vaccination of indoor cats will probably get the majority of cats in more trouble, not less!