Researchers uncover clues to deadly 1918 flu pandemic

The deadly 1918 pandemic flu spread faster than any other illness in recorded history – and now researchers may understand why.

In a new study lead by the University of Arizona (UA), researchers sought to understand the 1918 virus itself, as well as ways improve vaccination strategies and avoid future pandemics, Medical News Today reported. The 1918 flu virus killed more than 50 million people— three times the number of people who died in World War I.

Typically, the human influenza A virus is most threatening to infants and the elderly, but the 1918 virus killed many young adults, puzzling scientists. To understand this, researchers developed a technique that analyzes the rate at which mutations build up in specific parts of DNA. This “molecular clock” allowed them to reconstruct the 1918 pandemic virus’s origins, as well as those of the classic swine flu and the postpandemic seasonal H1N1 flu virus that circulated between 1918 and 1957.

They found that the 1918 strain originated from a human H1 virus that had been circulating among humans since around 1900.  This virus then picked up genetic material from a bird flu virus.

When the immune system is exposed to a virus, it reacts to the proteins on the surface of the virus and creates antibodies to prevent future infection from similar viruses. But when a new strain is genetically altered from previous strains to which the body has been exposed, the body’s protective antibodies are less effective, making infection more likely.

Researchers suggest that the young adults affected in 1918 may have had protection, due to childhood exposure, from a H3N8 virus circulating in the population.  However, they were unprotected from the new pandemic strain, because their immune systems made antibodies for the original virus.

"We believe that the mismatch between antibodies trained to H3 virus protein and the H1 protein of the 1918 virus may have resulted in the heightened mortality in the age group that happened to be in their late 20s during the pandemic,” said study author Michael Worobey, a professor in UA College of Science's department of ecology and evolutionary biology.

Their findings, published in the Proceedings of the National Academy of Sciences, suggest deaths from seasonal and new flu strains could be dramatically reduced by implementing immunization strategies that mimic the protection that early childhood exposure provides.

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