How Vaccines Work

A preventive vaccine is a substance that, when introduced into the body, teaches the immune system to detect and destroy a particular virus, bacterium or parasite that causes disease. It does so by stimulating an immune response against such pathogens. 

Vaccines can be made from whole killed pathogens, from pathogens that are alive but rendered harmless or from molecular fragments—known as antigens—that are derived from the pathogen of interest. Once used in vaccines, these components are all known as immunogens. These immunogens elicit powerful and typically specific immune responses involving T cells and antibody-producing B cells when introduced into the body. In generating this response, the immune system also amasses an army of memory B-cells and memory T-cells that quickly detect and neutralize the pathogen, should it ever reenter the body—and so prevent or diminish the sickness caused by that particular infection.

Vaccines can be introduced in different ways, including injection into the muscle, injection into or under the skin, application onto the skin, application to the inside of the nose, or by being swallowed. Vaccines can be made in a variety of ways, but only a handful of those approaches are applicable to the development of HIV vaccines. Learn more about the different types of vaccine strategies.