The fight-or-flight response. In reaction to stress, your body will either want to freeze or run away. For example, let’s say you suddenly see a bear in the park: you might experience the flight-or-fight response in reaction to seeing the bear because of the sudden stress you feel.
Because vaccines have healthy viruses that try to get your body to be immune to the diseases so when you are already sick your body won't respond to the vaccine because it's just more viruses
