The vast majority of people who test positive for coronavirus do not have any of the key symptoms of the condition, a study has suggested.
Some 77 per cent of people who received a positive result between late April and June had no symptoms on the day of their test, while 86 per cent did not have a cough, temperature or loss of taste/smell.
Researchers at University College London analysed data from the Office for National Statistics (ONS) coronavirus infection survey, which tests thousands of households every week regardless of whether people have symptoms.
The analysis looked at data for 36,061 people who had a test between 26 April and 27 June.
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Some 115 (0.32 per cent) had a positive test result, the study found, of whom 27 (23.5 per cent) were symptomatic and 88 (76.5 per cent) were asymptomatic on the day of the test.
When looking at the three main Covid-19 symptoms – a cough, fever and loss of taste/smell - 86.1 per cent of those who tested positive had none of these.
Professor Irene Petersen, who led the study, warned more widespread testing is needed as there could be many “silent transmitters” passing the disease on without realising they have it.
"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,” she told PA news agency.
She said university students are one group who should be tested regularly, especially before they go home for Christmas when they could “seed a lot of new infections” while indoors and sitting around the dinner table.
The researchers said there was a need to change testing strategies.
"Covid-19 symptoms are a poor marker of (Covid) infection," they wrote in the journal Clinical Epidemiology.
"In order to capture 'silent' transmission and potentially prevent future outbreaks, test programmes should involve frequent and widespread (Covid-19) testing of all individuals, not just symptomatic cases, at least in high-risk settings or specific locations."
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By contrast, Tim Spector, professor of genetic epidemiology at King's College London, who leads the Covid Symptom Study app, said data from more than four million people who used the app and reported symptoms over a week found 85 per cent of adults reported fever, cough or loss of taste/smell.
Although 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 per cent of cases in these important groups that were included in the ONS survey.”
While Paul Hunter, professor in medicine at the University of East Anglia, said the UCL study could not determine the proportion of people with Covid who become symptomatic or remain asymptomatic at some stage during their infection, due to the fact it looked at a fixed time point.
Additional reporting by PA