Live attenuated vaccine
A vaccine containing a weakened pathogen that can replicate in the recipient while usually causing limited disease, prompting an immune response.
Attenuation: The reduction of a pathogen’s ability to cause disease while retaining selected biological functions. Attenuation allows the vaccine strain to replicate without typically causing the full disease.
Measles vaccine: A vaccine that protects against measles, commonly delivered as part of the measles-mumps-rubella combination. Its live attenuated strain produces strong protection against measles.
Inactivated vaccine: A vaccine containing pathogens rendered unable to replicate, while retaining antigens that can stimulate immunity. Unlike live attenuated vaccines, it cannot reproduce in the recipient.
Immunocompromised host: A person whose immune defenses are weakened by disease, medication, or another condition. Uncontrolled replication can make some live vaccines unsafe for these people.
Innate immunity: The rapid, broadly acting immune defenses present before exposure to a particular pathogen. Replicating vaccine strains activate early defenses that shape later immune responses.
Oral polio vaccine: An oral vaccine containing weakened poliovirus strains that replicate in the intestine. It demonstrates how intestinal replication can generate mucosal immunity and reduce virus transmission.
Subunit vaccine: A vaccine made from selected pathogen components rather than an intact pathogen. It presents a limited set of antigens without introducing a replicating organism.
Pregnancy and vaccination: The clinical and public-health guidance governing vaccination before, during, and after pregnancy. Because of theoretical fetal risk, many live vaccines are avoided during pregnancy.
Adaptive immunity: Antigen-specific immunity mediated by B cells, antibodies, and T cells. The vaccine’s protection develops as adaptive responses recognize antigens made during replication.
Yellow fever vaccine: A vaccine made from the live attenuated 17D strain of yellow fever virus. The 17D vaccine is a durable example of protection from a weakened virus.