Originally Posted by ErbslinTrouble

it's really difficult to say. are you sure this is in the same place as the vaccine? some vaccines are given at the scruff of the neck or on the back on the side of the leg, with kittens it's easier to do at the scruff as there is more skin tissue and it's easier to keep them still. are you sure your kitten's injection was given at the hind side? might be a question to ask your vets to determine where the injection was. it's also possible it could be a lymph node that is swollen from the antibodies from the injection. is it on the back on the hind thigh above the lower leg joint? (run your finger down the back of the leg from the tail before the 'knee' joint) is this where you are refering to? or more on the side closer to the spine?