A new study sheds light on the flu’s yearly course around the world, helping scientists refine vaccines.
Each February the World Health Organization announces the strains of influenza expected to circulate in the Northern Hemisphere the following winter—and thus identifies which should be targeted by the year’s flu vaccine. WHO’s projection requires calculated guesswork; the flu virus is constantly evolving, accumulating small mutations through a process called antigenic drift. What’s more, because it takes months to make, test and distribute the flu shot, the forecast must be made nearly a year in advance. The stakes of prediction are high; each year, seasonal flu sickens hundreds of millions of people and kills some 500,000.
A recent study published in Science sheds new light on how flu viruses evolve and migrate around the world. Armed with this knowledge, scientists may be able to refine their forecasts of the flu strains most likely to cause epidemics and to better select viruses for the vaccine.
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