Well, first of all, let me say how sorry I am your Calvin got so sick from the shots. At least I assume his sickness came from the shots, but maybe he reacted like that 'cause the vet visit has been too exciting for him - or he has just upset his stomach.

I think when you plan to move to the UK and want to take the kitties with you, you need your kitties being vaccinated regulary, otherwise they wouldn't allow you to bring them into the country.

When they are always kept indoors, I don't believe an annual rabies shot will be necessary once you are in the UK, but there are other virus diseases which a cat can pick up even as an indoor cat, for example when you had contact with an infected cat outside your home, virulent material could still be on your clothes and shoes in that case. I would ask your vet about it what he thinks is the best. I would also describe his behavior to him and ask if this could be an allergic reaction to one of the vaccines, and if there's an alternative product available.

I hope little Calvin will be fine soon!

Kirsten