Attenuated vaccine
vaccine that uses a weakened (or attenuated) form of the germ that causes a disease
An attenuated vaccine (or a live attenuated vaccine, LAV) is a vaccine created by reducing the virulence of a pathogen, but still keeping it viable (or "live"). Attenuation takes an infectious agent and alters it so that it becomes harmless or less virulent. These vaccines contrast to those produced by "killing" the pathogen (inactivated vaccine).
Attenuated vaccines stimulate a strong and effective immune response that is long-lasting. In comparison to inactivated vaccines, attenuated vaccines produce a stronger and more durable immune response with a quick immunity onset. They are generally avoided in pregnancy and in patients with severe immunodeficiencies. Attenuated vaccines function by encouraging the body to create antibodies and memory immune cells in response to the specific pathogen which the vaccine protects against. Common examples of live attenuated vaccines are measles, mumps, rubella, yellow fever, varicella, and some influenza vaccines.
Development
Attenuated viruses
Viruses may be attenuated using the principles of evolution with serial passage of the virus through a foreign host species, such as:
Tissue culture
Embryonated eggs (often chicken)
Live animals
The initial virus population is applied to a foreign host. Through natural genetic variability or induced mutation, a small percentage of the viral particles should have the capacity to infect the new host.
This brief starts where responsible research should: with the source description of “Attenuated vaccine” as vaccine that uses a weakened (or attenuated) form of the germ that causes a disease. Everything that follows is an evidence route, not borrowed authority.
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Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated May 26, 2026. The linked authority identifier is Q1810913. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Attenuated vaccine” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.