from what I hear, they choose 6 or 7 of the most likely flu
strains that will hit your nation and
ones which can have the virus cultivated in an egg
. The viruses are harmless though, they are not meant to harm you in any shape or form. All they are meant to do is trick your immune system into making the right shaped cells to lock onto them, and attack them. However, I guess if most of your immune system is geared to the wrong types, then you could get into trouble.