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How do subunit vaccines stimulate an immune response?

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Infographic showing estimated lives saved by childhood vaccinations worldwide from 1974 to 2024, with syringe-shaped bars for each disease. Measles tops the list at 93.71 million lives saved, followed by tetanus, whooping cough, and others, for a total of 153.84 million lives saved. — vaccine Vaccines and the estimates of lives saved over the period 1974–2024.

Subunit vaccines stimulate an immune response by utilizing specific components of an infectious agent—most commonly proteins found on its surface—rather than the whole organism.12

These surface proteins act as antigens, which are the specific parts of a pathogen that the immune system recognizes as foreign. By introducing these isolated antigens into the body, the vaccine imitates an infection, prompting the immune system to produce antibodies against the infectious agent. This process allows the body to build immunological memory, ensuring that if the individual encounters the actual pathogen in the future, the immune system is prepared to recognize and fight it off.12

Because these vaccines contain only specific parts of the pathogen, they are incapable of causing the disease they are designed to prevent. In some cases, substances known as adjuvants may be used to further enhance the body's reaction to these antigens, helping to ensure a more robust immune response.13