Heterosubtypic immunity (HSI) is "cross-protection to infection with an influenza A virus serotype other than the one used for primary infection."Huan H. Nguyen et al, Heterosubtypic Immunity to Influenza A Virus Infection Requires a Properly Diversified Antibody Repertoire, Journal of Virology In layman's terms, an "infection with 'seasonal' influenza A viruses could induce immunity against unrelated sub-strains.""Winter flu could help protect kids". Leicester Mercury. 30 October 2009
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