How do vaccines work and how do they evaluate the impact on disease prevention?

Vaccines work by introducing a harmless component of a pathogen, such as a protein or an inactivated virus, to stimulate the immune system to recognize and combat the actual pathogen if encountered in the future. This process trains the immune system to develop a memory response, leading to quicker and more effective reactions upon exposure. The impact of vaccines on disease prevention is evaluated through clinical trials and ongoing surveillance, which assess their efficacy, safety, and the reduction in disease incidence within populations. Statistical analyses help determine the correlation between vaccination rates and decreased rates of infection, hospitalization, and mortality.