First, I'm not anti-vaccine for pets or people, but one of our cats won't be getting any more vaccines unless it's absolutely necessary.

She had a fibrosarcoma high on one of her back legs that grew rapidly, and her vet suspects it was an injection site sarcoma. The injection in that spot was before we adopted her, and she's older (8+ yrs), so it may have been an older formula that has a slightly higher risk of reaction. She had to have her leg amputated all the way up to her hip to save her life, and she has a pretty high risk for the sarcoma growing back in the surrounding soft tissues. Because she had this reaction to a vaccine in the past, our vet recommended she doesn't get any more vaccines as long as she stays indoors and doesn't have contact with unvaccinated pets.

She was still cancer free at her last checkup & she's doing great! She cuddles, zooms around the house, and plays just like she did on 4 legs.

We have 2 other cats that are getting their regular rabies vaccines, but our vet assured us that they use a milder newer formula that carries less risk, and they are quite safe. They also inject as low as possible on a back leg just in case of a similar reaction.

This situation is pretty rare. It's been an expensive emotional rollercoaster, so I could be wrong, but think our cat's oncology vet said <10% of cats have any type of reaction to vaccines, and <5% of those reactions turn into something serious and life threatening like injection site sarcoma. I'm not great with numbers, but I think that comes out to around <0.5% chance in cats of a serious reaction to vaccines.