A vaccine is a biological preparation that provides immunity to a specific infectious disease. It typically contains weakened or inactive parts of a germ, or its toxins, which stimulate the body's immune system to recognize and fight the disease. Vaccines help prevent illnesses like measles, influenza, and COVID-19. When a person receives a vaccine, their immune system learns to recognize the germ and can respond more effectively if exposed in the future. This process helps protect not only the vaccinated individual but also the wider community by reducing the spread of diseases, a concept known as herd immunity.