vaccinesattenuated

Attenuated vaccines, or live attenuated vaccines, use live microorganisms that have been weakened so they no longer cause disease in healthy individuals. The goal is to resemble a natural infection closely enough to provoke a strong and durable immune response.

Because the vaccine organisms replicate to a limited extent in the host, these vaccines typically induce robust humoral and cellular immunity and can provide long-lasting protection after few doses. They often generate mucosal immunity as well, which can contribute to protection at entry sites such as the respiratory or gastrointestinal tracts.

Common examples include vaccines for measles, mumps, and rubella (MMR); varicella (chickenpox); yellow fever; certain influenza vaccines given intranasally; and oral or injectable vaccines for rotavirus and tuberculosis (BCG). The oral polio vaccine is a historic example of a live attenuated vaccine. Attenuation is achieved through methods such as serial passage in culture or through genetic modification to reduce virulence.

Advantages of attenuated vaccines include strong, long-lasting immunity and often fewer required doses. They can provide better mucosal immunity and may offer herd protection. Limitations and safety considerations include a small risk of disease in the vaccine recipient, especially if immunocompromised or pregnant, and a risk of reversion to virulence in rare cases (notably in some polio vaccines). They require careful storage and handling to maintain viability, and some vaccines may pose transmission concerns if the vaccine strain spreads from a vaccinated person.