COVID-19 patients most infectious 2 days before, 5 days after symptoms emerge, analysis finds

SARS-CoV-2 viral load tends to peak during the first week of illness, making COVID-19 patients most infectious two days before symptom onset until about five days after, according to a recent study published in The Lancet

Researchers analyzed data on the viral load dynamics of MERS-CoV and SARS-CoV compared to SARS-CoV-2. The analysis evaluated 79 studies (5,340 people) on the novel coronavirus,11 studies (799 people) on MERS and eight studies (1,858 people) on SARS. The articles included in the analysis were published between Jan. 1, 2003 and June 6, 2020. 

SARS-CoV-2 viral load in the upper respiratory tract peaked in the first week of illness, while SARS viral load peaked between 10 and 14 days, and MERS viral load peaked between 7 and 10 days.

The analysis also found most individuals with asymptomatic SARS-CoV-2 tend to carry the same viral loads as those who are symptomatic, although those who were asymptomatic were able to rid the virus quicker than those experiencing symptoms. Additionally, researchers found a positive association between older age and longer infectious periods. 

While researchers found viral matter shedding for up to 83 days in the upper respiratory tract,  none of the SARS-CoV-2 studies in the analysis detected live virus beyond nine days of symptom onset. 



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