Immunological memory is the mechanism by

Position 1: This principle of immunological memory underpins the efficacy of vaccination, which deliberately induces a primary immune response so that protective memory is established without the individual suffering from the disease.

Position 2: During an initial infection, naive B and T lymphocytes that recognise the pathogen's antigens proliferate extensively and differentiate into effector cells that clear the threat.

Position 3: When the same pathogen is encountered again, these memory cells respond within hours rather than days, producing high-affinity antibodies before symptoms can develop.

Position 4: Immunological memory is the mechanism by which the adaptive immune system mounts a faster and stronger response upon re-exposure to a previously encountered pathogen.

Position 5: A subset of these activated cells subsequently persists in the body as long-lived memory cells, circulating in the blood and residing in lymphoid tissues for years or even decades.