I have a pony that has a bad reaction to her booster injections.  At first I thought it was the make of vaccine.  However, it happened twice.  So last time she needed her booster, I hacked her and her mother (who didn't have a bad reaction) to the local vet surgery.  They both had their injections and then walked home again.  I had no problem this time.  It may be, that she needed to be walked gently to dissipate the vaccine though her body.  Whatever, I saved my call-out fee. That is fine if you only have a mile or so to hack to the vets!