Table 1.
Significant Events of Relevance to Recent Human Pandemics.
| Year | Event | Segments | Resulting Pandemic/Panzootic Lineage |
| Pre-1918 | Host shift: ? to swine | ? | Classical swine (H1N1) |
| Pre-1918 | Host shift: ? to human | ? | Spanish flu (H1N1) |
| 1957 | Host shift: avian to human | H2, N2, PB1 | Asian flu (H2N2) |
| 1968 | Host shift: avian to human | H3, PB1 | Hong Kong flu (H3N2) |
| 1977 | Reintroduction of human H1N1 virus | All segments | Russian flu (H1N1) |
| Late 1970s | Avian to swine | All segments | Eurasian swine (H1N1) |
| Late 1990s | Host shift: human to swine | H3, N2, PB1 from human | Reassortant swine (H3N2) |
| Late 1990s | Host shift: avian to swine | PA, PB2 | Triple-reassortant swine (H3N2) |
| Pre-2009 | Mixing between swine | H1 from classical swine; N1, M from Eurasian swine; NS, NP, PA, PB1, PB2 from Triple-reassortant | H1N1 |
| 2009 | Swine to human | All segments | Pandemic H1N1 2009 |