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expert reaction to latest ONS Coronavirus Infection Survey data on characteristics of people testing positive for COVID-19

The Office for National Statistics (ONS) have released the latest data from their COVID-19 infection survey.


Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“The part of this ONS bulletin that deals with the symptoms people had, or didn’t have, deals with those who tested positive for the virus that can cause Covid-19 with what ONS call a ‘strong positive test’. So those figures don’t consider people who have low viral loads, and would be less likely to pass on the infection to others. The results come from a representative sample of the community population of the UK, who are tested only to investigate the spread of the virus, and not because of any symptoms they might have, or the jobs they do, or anything like that. ONS found that, in August this year, 42% of those who had a strong positive test result did not report any Covid-19 symptoms at all. That isn’t just symptoms on the day they tested positive – it’s any symptoms within 35 days of that positive test. So it seems likely that most of this 42% wouldn’t have even known they were infected, if they hadn’t been tested within the ONS survey. In other words, around four in every ten people who were infected with the virus, with a high viral load so that it’s relatively likely they could pass it on, seem not to know they are infected. Currently, the dashboard at is reporting about 30,000 new confirmed cases a day, and most of them will have symptoms – but these ONS figures indicate that, as well as the 30,000 confirmed cases, there could well be around 20,000 new infections each day of people who don’t have any symptoms, across the country.

“People should ask themselves, could they be infected without knowing it? Could they be passing the virus on to their friends, family, or people they don’t know who have weak immune systems so that the vaccines would not have been effective for them? I think that, among other precautions one could take, this is a pretty strong argument for wearing masks in indoor or crowded places – the evidence that masks reduce the risk of passing the virus on to others is pretty strong.”



Coronavirus (COVID-19) Infection Survey, characteristics of people testing positive for COVID-19, UK: 22 September 2021


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


Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic.  My quote above is in my capacity as an independent professional statistician.”

None others received.

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