Orchard Vet's Blog

Vaccine-related sarcomas


A client has recently spoken to us about their concerns over vaccine-associated sarcomas in cats. They had read about the adverse reactions that can sometimes occur where an animal has been injected. These include tumour growth (sarcomas), which can develop months after a vaccination.

Any treatment carries some risk, and these always need to be weighed against the benefits of protecting your pet from potentially fatal disease. There is a risk of injection site sarcomas but it is extremely small - the most recent study putting it as less than 1 in 30,000 doses - so for the vast majority of patients vaccinations are risk free. The most likely cause is inflammation associated with the administration of the injection and not the vaccine itself. Intriguingly, while injection site sarcoma has been reported in dogs it is incredibly rare even compared to its occurrence in cats.

By contrast there are significant benefits in having your cat properly vaccinated. Vaccines help the immune system fight infections from disease by stimulating the cat to produce antibodies against that disease. This process may make a cat seem lethargic or have a temperature for a few hours post-vaccination: side effects that are temporary and in no way life-threatening - in fact they're good because they demonstrate stimulation of the immune system. Likewise there may be slight inflammation at the injection site for a week or two, but this is quite normal. Once those antibodies are in the animal's system, however, it will be able to produce them to fight subsequent and potentially fatal infections.

Consequently the benefits of properly vaccinating cats far outweigh any potential risk of developing a sarcoma. However, if you still have concerns, please discuss them with your vet rather than abandoning a programme of vaccinations for your pet. §