Awww, poor darling
I'd just keep a close eye on him, make sure that he's staying hydrated and try to keep him calm. If he continues to vomit, then it may be time for the emergency vet. That's a big day for a little one, and with all the vaccinations, it might have been too much for his little tummy.
Keep us posted. I'm sure that someone more experienced than me will come along soon with some great advice
