I understand why you want the shot. It is probably a very good idea in your area. I would just keep a close eye on him after the shot and if it doesn't agree with him then I wouldn't do it again. Maybe they have made scientific advancements in the shot since my dog had it.
Angel (my 12 lb. poodle) got feverish and sick to her stomach. It lasted until about 24 hours after the shot was given. But you know their little bodies all react differently to these things. Maybe Angel was just alergic.
Let me know how it goes.