Hello. I have a kitten who is 7 months old. She received her first two distemper vaccinations already (the last one was in September) but she hasn’t had the third. Do I have to start over/is it too late to get the third one?
The short answer to your question is most likely, but it depends on a few factors such as how old your cat was when it got its last vaccine. The immune system is not considered developed enough in a cat until it is 16 weeks old. This allows its immune system to capable of having a more longterm memory.
The reason for boosters is to build the immune competency of your cat and ensure longterm protection. For the panleukopenia vaccination (sometimes called feline panleukopenia) it is part of the core vaccines. This vaccine recommended to be boostered within 2-3 weeks until the cat is 16 weeks old according to the feline practitioners official vaccination guidelines: https://journals.sagepub.com/doi/pdf/10.1177/1098612X13500429
Some manufacturers of vaccines have different dates then these recommendations. Generally, a veterinarian that administered the vaccines will know the specific guidelines and if there are any exceptions though. For more information about vaccines, I also recommend this article for a general overview: https://www.vetbabble.com/cats/health-cats/vaccinations/
So, given what you’ve told me, I would recommend planning for 2 more visits to your vet to get the vaccines current, but they will be able to say for certain based on the above info.