We got two bengal crosses in august, we picked them up two days after they had there second vacsination, they both had lumps the size of golf balls, they were not on there neck but more on there sides, well above there ribs but very promenent below there spine but high up if you know what I mean ( hopefully you do ) it took 2 weeks for the swelling to subside. I have been told it's common but a worry to look at, I think in some animals the vaccination leaks into pockets of either fat or just under the skin, don't keep prodding the lumps, but they will take time to dissolve/subside. mine were fine, and now have no lumps.