I don't know medically, but I have always had tetanus shots (I travel a lot) to keep up to date and have never had a noticeable problem afterwards.
He can always have the tetanus shot if he does get hurt, I think it has to be immediate. Remember, tetanus causes death, it's not something to be ignored.
Though I've not heard not to take the flu shot either. The only shot I've heard to avoid is yellow fever.