Small Changes in Transmission Rate of Seasonal Influenza Virus Can Lead to Rapid Evolution of New Strains, Model Shows; Results Lend Further Support to Importance of Surveillance of East, South, and Southeast Asia, and Other Densely Populated Regions

A computer model developed by scientists at the University of Chicago shows that small increases in transmission rates of the seasonal influenza A virus (H3N2) can lead to rapid evolution of new strains that spread globally through human populations. The results of this analysis, published online on September 14, 2016 in the Proceedings of the Royal Society B, reinforce the idea that surveillance for developing new, seasonal vaccines should be focused on areas of east, south, and southeast Asia where population size and community dynamics can increase transmission of endemic strains of the flu. The open-access article is titled “Explaining the Geographical Origins of Seasonal Influenza A (H3N2).” “The transmissibility is a feature of the pathogen, but it’s also a feature of the host population,” said Sarah Cobey, Ph.D., Assistant Professor of Ecology and Evolution at the University of Chicago and senior author of the study. “So a host population that potentially has more crowding, larger classroom sizes for children, or even certain types of social contact networks, potentially sustains higher transmission rates for the same virus or pathogen.” There are four influenza strains that circulate in the human population: A/H3N2, A/H1N1, and two B variants. These viruses spread seasonally each year because of a phenomenon known as antigenic drift: they evolve just enough to evade human immune systems, but not enough to develop into completely new versions of the virus. The H3N2 subtype causes the most disease each year. Genetic sequencing shows that from 2000 to 2010, 87 percent of the most successful, globally-spreading strains of H3N2 originated in east, south, and southeast Asia. Dr.
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