Viral Evolution

What made Spanish flu so deadly

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Science  06 Jun 2014:
Vol. 344, Issue 6188, pp. 1129
DOI: 10.1126/science.344.6188.1129-d

Spanish flu killed many young adults.

PHOTO: © EVERETT COLLECTION HISTORICAL/ALAMY; © BETTMANN/CORBIS;

The deadly pandemic Spanish flu of 1918 killed many millions, but unlike most flu strains, it targeted young adults rather than infants and the elderly. The reason remains a mystery. Worobey et al. used genetic and evolutionary approaches to infer that for much of the 19th century, a flu virus strain containing the same subtype of the hemagglutinin protein (H1) as the Spanish flu infected children. This gave them good immune protection from subsequent infections with H1-containing viruses. But from 1880 to 1900, the H3 subtype replaced H1 in circulating flu strains, and so people born between these times were less immune to H1. Around 1907, a novel H1-containing flu emerged, eventually becoming the deadly 1918 pandemic. With little protective immunity to H1, young adults exposed only to H3 subtypes during childhood suffered the greatest mortality.

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1324197111 (2014).

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