When you get a flu shot the vaccine is obtained by growing virus strains in chicken eggs, since the growing chick embryo reacts to the infection and produces the antidote. Of course, the chick does not survive. But the intention is to extract a vaccine that can save people from the inconvenience (or serious illness) of getting the flu. Problem always is they have to predict 6 months ahead of time what strain or two or three of flu virus will be the one or ones that will threaten to become epidemic those 6 months later. Not infrequently they miss the target and the flu shot is only effective against virus strains that are unfortunately not the one or ones that you encounter (which generally isn't reported for public consumption), so then getting a flu shot would have just as much chance of producing flu-like symptoms in you as a reaction to the shot, as it does to keep you from catching the flu at all.
What is turning into a worse problem is the zika virus, because it's spreading beyond the geographical limits of where observers had thought it was confined in years past. And when a pregnant woman catches it, her baby could have severe effects. Very tragic problem.