J.W.
I think it is more common than most doctors would like you to believe. My husband has only had the flu twice in his 32 years, but both times was right after having the flu shot. I would suggest speaking to your doctor as soon as possible. If his temp goes up quickly to 104 or higher, I would take him to the ER. If he got the flu from the shot, they have an anti-viral that can make him feel better much faster. However, it has to be started 24-48 hours after symptoms of the flu arrise. Good luck to you and I hope it is just a minor reaction.
J.