My son who is not diabetic had a very rare side effect from the flu vaccine last year. He had a very high temperature within 24 hours of having the jab and shortly after this noticed that one of his pupils stayed small even in a dim light. He had several tests and check ups to make sure nothing more sinister was behind this, nothing was found. It was likely to be a mild case of Guillain Barre syndrome which can in rare cases be triggered by the flu vaccine. However if he had had the flu his symptoms would have been much worse.
My son had this year's vaccination a week ago and apart from feeling a little off colour for a day or so has had no reaction this time.