Respuesta :

after your first exposure to a pathogen, you have memory T cells that will remember the antigen of the pathogen son in the future if you would come in contact with the same pathogen your body will recognize it right away and be able to kill it much faster
The second time your body is exposed to a pathogen you would have built a resistance to from the first time you were exposed to it. The same concept is applied when you are given a flu vaccine. They give you a very small nonliving version of the flu that doesn't harm you but prepares you for when you get infected with it so you are able to fight it off.