Q&A: COVID-19 Infectiousness Peaks Early in Sickness, Study Shows

Patients’ viral loads are highest within five days of their first symptoms, emphasizing the need to isolate early to prevent transmission.

Max Kozlov

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Since early March, a number of studies have suggested that patients infected with SARS-CoV-2 generally have a long incubation period and are most infectious early on in their sickness, with viral loads dropping off after nine days. These results have informed guidelines put forth by public health bodies, such as the US Centers for Disease Control and Prevention, which recommend that people isolate for at least 10 days following a positive COVID-19 test.

A meta-analysis published November 19 in The Lancet Microbe reviewed 98 studies on coronaviruses—79 of which focused on SARS-CoV-2 and the rest on SARS-CoV and MERS-CoV—to determine when patients’ viral loads are highest and could therefore transmit the virus most effectively. Of the SARS-CoV-2 studies, 73 included hospitalized patients only.

Their report finds that patients with COVID-19 show the highest amount of live virus in the upper respiratory tract within the first five days ...

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Meet the Author

Max Kozlov
Max is a science journalist from Boston. Though he studied cognitive neuroscience, he now prefers to write about brains rather than research them. Prior to writing for The Scientist as an editorial intern in late 2020 and early 2021, Max worked at the Museum of Science in Boston, where his favorite part of the job was dressing in a giant bee costume and teaching children about honeybees. He was also a AAAS Mass Media Fellow, where he worked as a science reporter for the St. Louis Post-Dispatch. Read more of his work at www.maxkozlov.com.
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