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| Year | Residue 89 in HA2 (percentage) |
| 1918–2005 | L (100%)* |
| 2006 | L (62.2%) and I (37.8%) |
| 2007 | L (65.9%) and I (34.1%) |
| 2008 | I (100%) |
Human H1N1 HA sequences with residue 89 in HA2 in database (www.fludb.org/brc/home.do?decorator=influenza) were compared for the evolutionary changes of residue 89.
*: Except M89 in A/Denver/1/1957 HA2, and I89 in A/Canterbury/106/2004 HA2.
