Does flu vaccine have any side effects?

Flu vaccines are very safe. The commonest problem after vaccination is slight soreness of the arm at the point where the injection was given; and less often, slight temperature and aching muscles can occur for a couple of days, but this responds easily to remedies like paracetamol. The risk of more serious reactions is extremely small - of the order of one in a million, or less; and considerably smaller than the risk of serious complications from the illness itself.