What is a vaccine and how does it speed up the immune response?

A vaccine is a biological preparation that provides acquired immunity to a specific infectious disease by introducing a harmless component of the pathogen, such as a weakened or inactivated virus, protein subunit, or mRNA. This exposure trains the immune system to recognize and respond more efficiently to the actual pathogen if encountered in the future. By stimulating the production of memory cells and antibodies, vaccines enable a quicker and stronger immune response, significantly reducing the severity of illness or preventing infection altogether.