What is the purpose of vaccines and how do they protect against diseases?

Vaccines are an important tool for preventing infectious diseases. The purpose of vaccines is to stimulate the body's immune system to recognize and defend against specific disease-causing pathogens. Vaccines contain a small amount of a weakened or inactivated form of the pathogen, or pieces of the pathogen, that cannot cause the disease but can still trigger an immune response. When the immune system encounters the vaccine, it produces a response that includes the production of specific antibodies that recognize and neutralize the pathogen. This immune response is similar to what would occur during a natural infection, but without causing illness.

Vaccines protect against disease by preparing the immune system to respond quickly and effectively to the pathogen if it is encountered again in the future. If a vaccinated individual is exposed to the disease-causing pathogen, their immune system is able to quickly recognize and destroy it before it can cause illness. This not only protects the vaccinated individual, but also contributes to herd immunity, which is the indirect protection of unvaccinated individuals because there are fewer opportunities for the disease to spread through the population.