I was wondering if I could seek some opinions from some fellow cat owners. My cat William is 18 years old and now living as an indoor cat. We inherited him from my in-laws and aside from a couple of visits to vets for fighting related incidents (!) He's never been otherwise.
He had a check up recently, they noticed a bit of muscle wasting in back legs and I have observed some head twitches / shakes recently (not ear mites or infection) so may be something else. Otherwise he eats and drinks fine, plays and interacts same as usual and uses litter tray fine. The vet said they are happy he is in good health to have feline enteritis and influenza vaccination next week and booster 3 weeks after.
The only reason I asked about it is we are thinking of going away and found a lovely 'cat hotel' one of the Longcroft ones, to take care of him l went to visit and it looks lovely. But he has to have these vaccines as conditions of stay. No local family or friends to look after him and partner not comfortable with a pet sitter in our house.
I was wondering what others opinions are about vaccinating old and indoor only cat? Is it risky, anyone had side effects with their cat? I am asking as feel guilty as we are only doing it to benefit us to board him and would hate for something bad to happen as a result

I would much rather not have a holiday and just stay at home if the vaccine could cause him harm in anyway.
Would other people bother vaccinating old indoor cat unless they had to board him?
Any advice or opinions much appreciated. X