What long term ( as in more than a few years) effects are there for a flu shot? what will 20 years of flu shots do to their bodies? or their children?

Zero/zero: The flu vaccine is just a fancy way to avoid illness that you might otherwise get. It challenges your immune system when you take it, just like the colds & flu you have normally.Your body builds a immune memory & gradually has less symptomatic illness as you age. Infants gain a passive benefit from mom's immunity that protects them for many months.