My small dog had a rabies shot last week and now she has a lump on the back of her neck. Will this disappear or should I be worried?
You probably have nothing to worry about. It is quite common for dogs to develop small masses (lumps) under the skin in areas where vaccines have been administered.
In dogs, most of these lumps are localized areas of immune system activity triggered by the vaccine. Since the purpose of vaccines is to stimulate the immune system, such a response is generally not very surprising.
In my experience, the rabies vaccine is the most likely to cause these reactions. As well, the lumps seem more common in young, smaller dogs.
Most vaccine-associated lumps in dogs slowly resolve over several weeks. You should watch the area carefully. If the mass is growing or painful, it could be a more serious problem such as an injection site abscess or infection. If you have any doubts, have your vet check the site.
Cat owners should be aware that vaccine-related lumps in cats often are not as benign in those in dogs. This is particularly true if a lump develops after a rabies or leukemia injection. In rare instances, this sort of lump can be a precursor to a tumor. Any lump at the site of an injection in a cat should be assessed by a veterinarian.