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expert reaction to preprint on estimates of rate of infection and asymptomatic cases

A preprint, an unpublished non peer-reviewed paper posted on medRxiv, estimated the of rate of COVID-19 infection and asymptomatic cases.


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

This is a useful, though relatively small (n=431) study targeting a very specific type of adult population (twins, which may not reflect the majority of the population), showing about one fifth (19%) of the participants were asymptomatically infected with SARS-CoV-2. The regular logging of their symptoms for 3 months prior to each visit would reduce any symptom recall bias/error.

“This asymptomatic infection rate seems lower than with this earlier England-based community adult population SARS-CoV-2 PCR surveillance study, which indicated that only about one-third (39/126) of PCR positive cases being symptomatic (as assessed in the 7 days prior to their swabbing) with a much higher two-thirds (87/126, 69%) being asymptomatic:

“The differences may be due to natural variations in immune responses to the virus across these different populations – and perhaps how the different study participants were asked/answered questions about their symptoms.

“But the main outcome is that asymptomatic infection and transmission is a real phenomenon – which will make this COVID-19 pandemic difficult to control – as we are seeing both in the UK and globally – as already recognised by the WHO in this recently updated 9 July 2020 Brief:

“Based on what we currently know, transmission of COVID-19 is primarily occurring from people when they have symptoms, and can also occur just before they develop symptoms, when they are in close proximity to others for prolonged periods of time. While someone who never develops symptoms can also pass the virus to others, it is still not clear to what extent this occurs and more research is needed in this area.””


‘Estimates of the rate of infection and asymptomatic COVID-19 disease in a population sample from SE England’ by Philippa Wells et al. is a preprint on medRxiv.


All our previous output on this subject can be seen at this weblink:


Declared interests


None received.

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