Though my dogs have not had a reaction to a vaccine, I tend to err on the side of caution when it comes to vaccines. I would rather give a benadryl to help prvent a reaction then wait and hope for the best. I say this because my cat had a severe vaccine reaction after his rabies shot. Within 20 minutes of the shot he was vomiting, the hair at the vaccination site fell out and the site became swollen. We had to rush him back to the vet to be treated for the reaction.
