Vaccines are medical products designed to stimulate the body's immune system to recognize and fight specific diseases. They often contain weakened or inactive parts of a particular germ, such as a virus or bacteria, which helps the body learn to defend itself against future infections. Vaccines are crucial in preventing outbreaks of diseases like measles, polio, and influenza. When people receive vaccines, they develop immunity without suffering from the actual disease. This not only protects the vaccinated individual but also helps create herd immunity, which can protect those who cannot be vaccinated, such as infants or individuals with certain health conditions. Vaccination programs have significantly reduced the incidence of many infectious diseases worldwide.