I keep in walk for that day, and don't let them get hot and bothered for 3 days. I don't give days off though.
TBH, they normally have the rest f the day off after the vaccination, but if I wanted to give them a walk out, that would be OK. The day after I would be happy for a bit of schooling, but a lighter session, so as not to make them hot and bothered.
I think the vaccination themselves have been updated so you can now ride as normal. Because I've had horses for so long , and the old advice was give a day off after, I still do!
I give mine a few days off but keep him walking. He gets turned out and then walked out in hand when he would normally get ridden. Mine suffers badly from inflammation at the injection site so doing as little as possible but keeping him moving to drain the fluid is the best for him.
The old advice used to be the next day off and I still follow that to be honest. I feel sore after a jab, so I tend to think (rightly or wrongly) that a horse might feel a bit sore too.