I don't , they get one day off and quiet for three days the fitter they are the more they seem affected ,I now have antinflammatories given on the day to ones that seem affected.
We always use to go by the light work that doesn't make them sweat but at the last jabbing we were told strictly no exercise for 24 hours, so that's what we did.
The RVC (Royal Veterinary College) recommends no strenous excercise after vacinations for 24-48 hours, and under the rules of the Jockey club I think I read they are not allowed to be race for 8 days after.
The horse should have done no heavy exercise for two hours prior to the vacinnation and the horses coat should be clean and dry!