The mechanism of action for vaccines involves stimulating the immune system to produce a protective response against specific pathogens. Vaccines contain weakened or inactive forms of the pathogen, or components such as proteins or sugars that resemble parts of the pathogen. Once administered, they prompt the immune system, particularly B and T lymphocytes, to recognize these components as foreign. This initiates the production of antibodies and the activation of memory cells. Consequently, if the individual later encounters the actual pathogen, their immune system can respond swiftly and effectively, providing immunity and preventing disease.