For the first time ever, I had a reaction to my yearly flu shot about 24 hours after I got it. Even as bad as I felt last night (chills, sweating, headache, plus a stomach bug that I don't think was technically related), I knew it would pass quickly. I am now living with a Type I diabetic and it is imperative that he doesn't catch the flu, which can be deadly for him. He HAS to get his flu shot tomorrow, no more putting it off, as it takes about two weeks to really kick in!