My cat lost a patch of hair at the area of her vaccination. She is 10 years old and this has never happened before.We took her to the vet and they said that it's an allergic reaction and that next time they'll do it in the muscle. However, now there is also a tiny wound at the injection area. Should I be concerned or is it possible that my cat bit herself while cleaning the area? Is it worth a trip to the vet's?