The main function of a vaccine is to stimulate the immune system to recognize and combat specific pathogens, such as viruses and bacteria. Vaccines contain weakened or inactivated parts of an infectious agent, or a blueprint (like mRNA) for producing a harmless piece of the pathogen. When administered, they train the immune system to identify and respond to the actual pathogen quickly and efficiently, should exposure occur in the future. This helps prevent the spread of infectious diseases and protects individuals and communities from outbreaks. Vaccination is a critical public health tool that has significantly reduced mortality rates from various diseases.