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Covid-19: Why are age and obesity risk factors for serious disease?

BMJ 2020; 371 doi: (Published 26 October 2020) Cite this as: BMJ 2020;371:m4130

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  1. Elisabeth Mahase
  1. The BMJ

Worldwide more than 41 million people have now been infected with SARS-CoV-2 and over a million people have died. But what makes this virus so difficult to control, and why are some people more at risk than others? Elisabeth Mahase reports

Why is it so hard to stop SARS-CoV-2 spreading?

Paul Lehner, professor of immunology and medicine at the University of Cambridge, says that unlike the original SARS coronavirus or influenza, people with SARS-CoV-2 are most infectious before they become unwell, normally about a day before they develop symptoms.

“So you’re maximally transmitting virus while you’re feeling well,” he told a Science Media Centre briefing in London on 22 October. “This is a really brilliant evolutionary tactic of the virus. It means you can be out at the races, in a pub, singing in the church choir, at a matriculation—you’re feeling well.

“This is a hit and run virus . . . The question then becomes: how can you make so much virus and yet feel well?”

Lehner explains that the answer lies in the virus’s ability to switch off cells’ natural response to it. “SARS-CoV-2 knows all about …

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