The findings by National Institutes of Health scientists are said to have important implications for monitoring changes to such viruses and predicting which strains should be used for flu vaccine.
In an effort to better understand how seasonal influenza evolves into new strains, the researchers analyzed the genomic sequences of the two most common flu strains -- H3N2 and H1N1 -- from the 1995-2005 flu seasons in New York state and New Zealand.
The sequence data was obtained from the Genome Sequencing Project, which recently generated more than 1,000 fully sequenced influenza genomes from clinical isolates.
The analysis reveals a picture of flu evolution that is surprisingly different from the prevailing conception of how the viruses change.
For example, evolution of the influenza A virus is commonly viewed as a typical Darwinian process. Unexpectedly, however, the study found the periods of intense Darwinian selection accounted for only a relatively small portion of H3N2 flu evolution during the 10-year period examined.
The entire study is detailed in the online journal Biology Direct.