A substance made of weakened or dead pathogens, it gives the body immunity against disease. Vaccine. A vaccine helps your body learn how to fight infections by introducing a harmless form of a germ, so you're protected if you encounter the real thing.
Imagine you're preparing for a big exam by taking practice tests that mimic the real thing. Just like these practice tests help you get familiar with the exam format and questions, a vaccine introduces your immune system to a weakened or dead version of a pathogen, so it knows how to respond when faced with the actual disease. In this analogy, the practice tests are like the weakened or dead pathogens in the vaccine, training your immune system (like your brain for the exam) to recognize and effectively deal with the real threat, providing you with immunity against the disease.
