The flu season is not here yet but, according to the CDC, the flu season never ends. Their “Flu View” still reports occurrences as late as May nationally.
Each year it is recommended that everybody get a flu shot. There are many vaccines from different viruses available and each year new viruses are detected and new vaccines have to be made. The safety of these vaccines, all with possible side effects, is not and cannot be properly studied because what a current year’s viruses are is not known beforehand.
Side effects can be severe, especially in children under three years of age, or in anybody for that matter.