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Early life environmental exposures play key roles in our ability to launch an effective immune response due to a phenomenon referred to as “immunological imprinting” – the process by which the immune system fights infections after previous exposure to a pathogen. A commonly held theory was that previous exposure to an influenza virus conferred no immunological protection against subsequent exposure. However, new data suggest that immunological imprinting due to exposure to subtypes of influenza viruses during childhood may provide partial lifelong protection against other subtypes.
Influenza is a highly contagious respiratory infection caused by the influenza virus. Complications from influenza sicken or kill hundreds of thousands of people worldwide each year. Although children and elderly people are typically among the most vulnerable to influenza infection, some subtypes of influenza disproportionately affect young, healthy adults.
The authors of the study analyzed large surveillance data sets from the Arizona Department of Health Services, spanning 22 years of influenza seasons. The Centers for Disease Prevention and Control define “influenza season” as occurring between epidemiological week 40 (usually early October) of one year and week 39 of the subsequent year.
Their analysis revealed that immunological imprinting shapes a person’s seasonal influenza risk and emphasized that childhood exposures can imprint a lifelong immunological bias toward particular influenza subtypes. However, newer antibody responses acquired later in life did not provide the same strength of protection as responses imprinted in childhood following the first exposure. The authors of the study postulated that the low mortality rates associated with some influenza subtypes may increase as cohorts of exposed people age.