<unk>  (HSI) is defined as cross-protection to infection with an influenza A virus serotype other than the one used for primary infection." In layman's terms: an 'infection with "seasonal" influenza A viruses could induce<unk>  against unrelated sub-strains.'
Heterosubtypic immunity
Immune tolerance
Herd immunity
Vaccine resistance
Peripheral tolerance
Antigenic variation
Antigenic escape
Host adaptation