I called J's pediatrician this morning and spoke to the nurse. She said the big red welt isn't unexpected since he fought the shots like a wild thing - she said that when that happens, the vaccine can go into a fatty pocket rather than right into muscle. She recommended massage and a warm compress to help that go down. The blisters were a puzzle to her, though. J got the DTaP, MMR and polio vaccines, not chicken pox, so we're not sure where the blisters came from. At any rate, we're going in tomorrow for the Hep A vaccine, so the doc can take a look at it then.
The blisters are gone, anyway - I think J must have popped them while he was squirming in his sleep.