Global Migration Dynamics Underlie Evolution and Persistence of Human Influenza A (H3N2)
Infections by the influenza A virus show highly seasonal patterns in temperate regions thus we typically call winter the flu season.
Infections by the influenza A virus show highly seasonal patterns in temperate regions thus we typically call winter the flu season. Over the course of autumn and winter, a small number of initial infections grow to encompass a significant proportion of the population with the infections then disappearing at the end of the winter season. It has been suggested that the strains founding each temperate flu season originate from China and Southeast Asia, where influenza A is less seasonal. This hypothesis was tested by analyzing genetic sequences from viruses sampled throughout the world between 1998 and 2009. From these samples it was found that although China and Southeast Asia play the largest role in the migration network, temperate regions, particularly the USA, also make important contributions and that not all temperate strains of influenza die out with the end of the winter season.
Instead strains migrate to more favorable climatic regions thus making patterns of influenza transmission highly dynamic. With this emigration out of temperate regions, mutations harbored by temperate strains of influenza A can spread to the global virus population. Which means that regional public health decisions regarding influenza may have global impacts. Thus the use of antivirals should be done with great caution as this practice can promote development of drug-resistant strains. On the flip side, the finding also means that vaccination programs outside of China and Southeast Asia can be effective in curbing influenza's spread globally. In addition, growing knowledge about patterns of flu migration eventually may make it possible to tailor vaccines to particular locations. For example South American regions get almost all of their flu from North America so rather than giving South America the same vaccine that the rest of the world gets their vaccines should be targeted against the strains isolated in North America for the given season.
