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How do live attenuated vaccines work?

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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.

Live attenuated vaccines work by utilizing a weakened form of a virus or bacteria that retains the ability to stimulate an immune system response without causing serious illness.12

Because these microorganisms are alive but attenuated, they multiply to a limited extent within the body, closely mimicking a natural infection. This process triggers a robust and effective immune response, leading to the production of antibodies and long-lasting immunity. By imitating a mild form of the disease, these vaccines provide some of the most effective prophylaxis available.13

While these vaccines are safe for healthy individuals, it is important to note that they may cause the full disease in people with immune deficiencies. Modern medical research has further refined this process by using recombinant DNA technology to genetically modify pathogens, allowing for the deletion or alteration of harmful proteins to create safer and more effective attenuated strains.32