How does vaccine protects disease?

Vaccines protect against disease by stimulating the immune system to recognize and respond to specific pathogens, such as viruses or bacteria. They contain weakened or inactivated parts of the pathogen, or genetic material that instructs cells to produce a harmless piece of the pathogen. This exposure trains the immune system to remember the pathogen, enabling a faster and more effective response if the body encounters the real pathogen in the future. As a result, vaccines significantly reduce the risk of infection and the severity of disease.