waningimmunity

Waning immunity is the gradual decline of immune protection against a pathogen after natural infection or vaccination. Over time, the immune system may provide less effective defense, increasing susceptibility to reinfection or to more severe disease, though some memory responses can persist and offer partial protection. Immunity consists of humoral components, such as antibodies, and cellular components, including memory B and T cells. Antibody levels commonly fall after an initial response, and the overall durability of protection depends on how well memory responses can be recalled upon exposure.

Several factors influence the durability of immunity. Time since the initial exposure or vaccination is a primary factor. Pathogen changes, such as antigenic drift, can reduce recognition by existing antibodies. Host factors, including age, health status, and immune system strength, also matter. Vaccine-related aspects, such as the type of vaccine, dosing schedule, adjuvants, and the use of booster doses, affect how long protection lasts. Different diseases exhibit varying durability of immunity; for example, some vaccines may confer long-lasting protection while others show more rapid waning.

Public health implications of waning immunity include the consideration of booster vaccination programs, vaccine reformulation to match circulating strains, and ongoing surveillance for breakthrough infections. Evaluating durability involves vaccine effectiveness studies, measurements of antibody levels, and real-world data on disease outcomes.

Examples in practice include waning protection against infection with certain respiratory viruses after vaccination, which can inform timing of boosters and annual reformulations for vaccines like influenza. Distinctions are made between waning immunity and primary vaccine failure or complete lack of prior exposure.