People are always allergic to something. I was allergic to a particular flavor of an artificial beverage in the 80's called CapriSun, but it may have been in combination with immune exposure to pollen, dirt, flu, seasonal cold, soap, laundry detergent, or any other random substance. I broke-out in hives.

My aunt has readily-lethal anaphylactic reactions to dozens of foods and other substances.

Epinephrine, diphenhydramine, albuterol, and famotidine should be readily available at all vaccine injection sites. Even with doing everything right, people who experience medical emergencies can and do still die.