My deceased EX was military. He was on what they called in the USAF the Prime Beef Team which was the teams they deployed first in emergencies to set up camps and the physical part of the unit's areas

The military would give them vaccinations quite often saying that it was protection for them if they had to go into other countries for diseases. These vaxxs would be a round of shots for idk how many different diseases all at the same time.

Every time he took them he would be deathly sick for days, I mean high fever, sweats, shakes, vomiting. just sick as hell.
This was when I was about 18 yrs old so I never have taken any flu shots.