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Strains of influenza responsible for pandemics spanning a centurya
| Period (yrs) | Pandemic | Strain | Species of origin of HA and NA genes |
|---|---|---|---|
| 1918–1923 | Spanish flu | H1N1 | Human |
| 1957–1958 | Asian flu | H2N2 | Avian |
| 1968–1969 | Hong Kong flu | H3N2 | Avian |
| 2009–2010 | 2009 A(H1N1) | A(H1N1) | Porcine and avian |
HA, hemagglutinin; NA, neuraminidase.
