nonimmune

Nonimmune is an adjective used in medicine and biology to describe the absence of protective immunity to a particular pathogen, antigen, or disease in a person, tissue, population, or organism. It indicates a lack of specific immune defenses, such as antibodies or memory T cells, against that agent, even though other components of the immune system may be present. Nonimmune status is distinguished from general immunocompetence; an individual can have innate defenses yet be nonimmune to a certain infection.

In clinical and public health contexts, nonimmune is often inferred from serologic testing that shows seronegativity (no detectable antibodies) or from a lack of protective immunity after vaccination. It is also used to describe populations with low immunity, such as newborns before acquiring maternal antibodies, people who have never been exposed, or those whose vaccine-induced immunity has waned. Nonimmune can be temporary or persistent, depending on exposure, vaccination, and immune system factors.

Implications of nonimmune status include increased susceptibility to infection and the potential need for protective interventions. Public health strategies may include targeted vaccination campaigns, booster doses, or heightened surveillance to prevent outbreaks in nonimmune groups. In individuals, nonimmune status can influence recommendations for exposure risk management and prophylaxis after potential contact with an infectious agent.

In research and laboratory contexts, nonimmune subjects or tissues are described as lacking antigen-specific immune responses and may serve as controls when studying immune mechanisms or evaluating vaccines and therapeutics. See also seronegative, immunity, and vaccination.