Most people who test positive for the coronavirus do not have symptoms at the time samples are taken, according to new research.
Data suggests that 77% of people had no symptoms on the day of their test, while 86% did not have any of the main warning signs – a cough, a temperature or a loss of taste or smell.
The results have led to warnings of “silent spreaders” of COVID-19 from the scientists who worked on the study.
But some academics urged caution over the figures, saying that people who had recovered from their symptoms or may go on to have them and then tested positive would be counted as not having signs of the coronavirus.
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The symptoms research was led by professor Irene Petersen at University College London and was based on information from the Office for National Statistics.
The study involved analysis of the data for more than 36,000 people who were tested between the end of April to the end of June.
Of these only 115 – 0.32% – tested positive for COVID-19.
Of these 27 – 23.5% – were symptomatic, while 88 – 76.5% – were asymptomatic on the day they were tested.
When looking at cough, fever and loss of taste/smell – seen as the main symptoms – 86.1% of those who tested positive had none of these.
Prof Peterson said people may have had symptoms in the days before their test or developed them later, but the figures suggested large numbers may be spreading the virus while asymptomatic.
She said: “They may be silent transmitters and they don’t know about it. And so I think that’s a problem.
“You may have a lot of people who are out in the society and they’re not self-isolating because they didn’t know that they are positive.”
Professor Tim Spector of King’s College London, who leads the COVID Symptom Study (CSS) app, warned that the research does not mean people will not have symptoms at all for the length of their infection.
He said data from more than four million people who used the app and reported symptoms over a week found that 85% of adults reported having a fever, cough or a loss of taste or smell.
He added: “But the data on children and the over-65s from the CSS app tell us a different story.
“Only using the UK’s three classic symptoms will miss around 50% of cases in these important groups that were included in the ONS survey.
“In a sub-study at King’s College London of twins using antibody testing and the ability to report 20 different symptoms, we showed that only 19% of people are truly asymptomatic.
“We need to learn from other countries and improve awareness of all the symptoms of COVID-19 to properly control the spread of the virus.”
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Professor Paul Hunter at the University of East Anglia said the UCL study could not show the proportion of people with COVID who become symptomatic or remained asymptomatic at some stage of their infection, as it only checked if they had external signs of infection when they actually took the test.
He said: “Anyone who was previously symptomatic and had now recovered or who were currently incubating the infection and would develop symptoms within the following hours would not be included as being symptomatic in this study.”
A government spokesman said ministers are aiming to increase testing capacity to 500,000 a day by the end of October.
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