Answer:
From previous knowledge I would expect your answer to be vaccines. What doctors do is get i dead sample of whatever virus they have already encountered and are expecting to return or for whatever is yet come. They get that sample and inject the dead virus in your body. This is for your body to then create Antibodies for that specific virus or sickness. That is why some people get sick when they get vaccine shot because their body is then fighting the dead virus and also creating new antibodies. people may get sick but they won't die from it because the sample is a weakened form.
Hope this helps <3!!
Step-by-step explanation: