Covid-19 has many faces

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ACCORDING TO England’s National Health Service the signs that someone has contracted the novel coronavirus SARS-CoV-2 are a high temperature or a new, continuous cough. This is certainly true for a majority of patients, but it is not so for a sizeable minority. Papers published in recent weeks present the new virus as having many faces. This is in stark contrast to the way in which influenza, another primarily respiratory disease, behaves—and it makes SARS-CoV-2 all the more dangerous. It also raises the question of why this virus’s symptoms are so protean.

For decades, influenza has been referred to as “an unvarying disease caused by a varying virus” because of its tendency to mutate every year and yet still cause the same symptoms of rapid-onset fever, malaise, headaches and coughing. Indeed, a review of influenza papers published in 2018 by John Paget of the Netherlands Institute for Health Services Research, showed that even when...