Multiple strains of the flu virus, circulating in a population at the same time, can reshuffle their genes and create a new virus, one capable of infecting many more people, according to a new study in the open-access journal PLoS Biology. This finding may help scientists make better predictions about which viral strains will attack during upcoming flu seasons and design more effective flu vaccines.
In the first large-scale effort to sequence the flu genome, Edward Holmes, David Lipman, and colleagues examined the genomes of 156 influenza A viruses (serotype H3N2) collected by New York State public health officials between 1999 and 2004. "We found that there are co-circulating minor variants that are not infecting many people," says Lipman. "One of these can become the next epidemic strain."
These co-circulating viruses can exchange genes in a way that creates novel, epidemiologically significant strains--a process that can occur when someone is infected simultaneously by more than one strain. The genetic reshuffling demonstrated in this study is the first to examine in detail a reassortment event from a persistently cocirculating minor strain to a previously dominant strain leading to an epidemiologically significant outcome--the emergence of the "Fujian" strain in the 2003-2004 flu season.