A new survey has found that over 80 per cent of positive coronavirus cases had no core symptoms at the time of testing.
The Office for National Statistics (ONS) Covid-19 survey, carried out between April and June, found that 86.1 per cent of people who tested positive during that time did not have any of the core coronavirus symptoms (a fever, cough or loss of taste or smell) when they took the test.
Three quarters of those who tested positive had no notable symptoms whatsoever on the day of testing, found scientists.
The finding has highlighted the prominent role that so-called "silent transmission" may be playing in the coronavirus outbreak, prompting fears that future outbreaks will be difficult to control without more widespread testing.
The ONS infection survey, unlike community testing for coronavirus, routinely tests thousands of households nationwide, regardless of symptoms.
“At the moment, the focus is on people who have symptoms, but if you are not catching all those who are asymptomatic or presymptomatic it may be really difficult to get outbreaks down in time, before they get out of control,” said Irene Petersen, an author on the study and professor of epidemiology and health informatics.
While some of the people who did not have core symptoms may have gone on to develop symptoms, Petersen warned that there is a risk of silent transmission by those unaware that they have the disease.
The study analysed the symptoms of over 36,000 people tested for coronavirus between April and June, Just 115 tests came back positive, with only 27 having symptoms of any type. Narrowing down symptoms to the three "core" coronavirus tells, the number reporting classic symptoms fell to just 16.
Regular testing to spot asymptomatic cases
Taking the findings into account, Petersen now argues that high risk workplaces and universities should conduct regular testing to pick up asymptomatic cases.
She urged university testing in particular ahead of Christmas, saying, “Anybody who’s had students coming home at Christmas knows they often bring some sort of bug with them and this Christmas in particular they could bring Covid home and potentially seed new outbreaks."
Patrick Maxwell, head of the school of clinical medicine at Cambridge, said that the study highlighted that many people with coronavirus are asymptomatic.
“There will be great public health benefit in terms of reducing transmission if we can reliably identify asymptomatic individuals and they then self-isolate,” he said.