Vaccines stimulate the immune system to recognize and fight specific pathogens without causing the actual disease. They contain weakened, inactivated, or parts of the virus or bacteria, which trigger the production of antibodies. When the vaccinated person encounters the real pathogen later, their immune system responds faster and more effectively, preventing illness. Vaccination also contributes to herd immunity, reducing disease spread in the community. Modern vaccines, like mRNA vaccines, teach cells to produce a harmless viral protein that triggers immunity. Overall, vaccines are a safe, effective, and essential tool for preventing infectious diseases.