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expert reaction to study comparing viral load of asymptomatic vs symptomatic people

A study, published in Thorax, looked at COVID-19 viral load of asymptomatic vs symptomatic people.


Dr Julian Tang, Honorary Associate Professor of Respiratory Sciences at the University of Leicester, said:

“This outbreak in Daegu, South Korea was back in March 2020, and since then many studies have shown the same thing – that viral load does not necessarily impact on clinical severity.

“In fact, SARS-COV-2 viral loads have been found to be similar across different age groups and different severities of COVID-19, from children to the elderly.  This new study is useful as further confirmation that the same is also true of 20-30 year-olds.

“COVID-19 is mostly a host-immune mediated disease – the viral load does not really impact on this in most cases. Not all ICU cases have high viral loads – in some, the virus has already cleared before they are even admitted to ICU.

“Asymptomatic cases can spread virus aerosols simply by breathing and talking, which may be the most common way we transmit this pathogen – even with just a typical viral load. 

“We breathe and talk a lot more than we cough, so if everyone wears masks in indoor areas in the presence of other people it will also contain the virus quite effectively in those who don’t even know they are infected, and reduce transmission.”


Dr Jeff Barrett, Senior Scientific Consultant, Wellcome Trust Sanger Institute, said:

“The samples taken for this analysis are an average of 13 days after initial diagnosis. We now understand that the total viral load drops off over this time period. The results therefore don’t support the statement that ‘they may have a key role in driving the spread of Covid-19’.  To make such a claim would require testing individuals at the peak of their infectiousness, not two weeks later.”



‘Upper respiratory viral load in asymptomatic individuals and mildly symptomatic patients with SARS-CoV-2 infection’ by Sang Hyun Ra et al. was published in Thorax at 23.30 hours UK time Tuesday 22 September 2020.

doi:10.1136/ thoraxjnl-2020-215042


Declared interests

None received.

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