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Asymptomatic people accounted for 86% of people who tested positive for COVID-19 in a UK population sample during the lockdown, a study showed Thursday, meaning that the current policy of screening people with symptoms could overlook many cases.
In England, people are encouraged to get tested for COVID-19 only if they have symptoms of a persistent cough, fever or loss of taste or smell, and contacts suspected of positive cases are told to self-isolate in the first instance.
But epidemiologists at University College London found that such an approach could miss the vast majority of cases, complicating Prime Minister Boris Johnson’s attempts to clamp down on a second wave of the virus.
UCL scientists used the Office for National Statistics Infection Survey, which looks at the prevalence of COVID-19 in the community and not just in those who are tested because they have symptoms.
The pilot study included 36,061 people living in England, Wales and Northern Ireland who were tested between April 26 and June 27.
Of the 115 with a positive result, only 16 reported symptoms, and 99 did not report any specific symptoms on the day of the test. Additionally, 142 people who reported symptoms on the day of the test did not test positive for COVID-19, far outnumbering those who tested positive.
“The fact that so many people who tested positive were asymptomatic on the day of a positive result calls for a change in future testing strategies,” said Irene Petersen of UCL Epidemiology & Health Care.
“More widespread testing will help capture ‘silent’ transmission and potentially prevent future outbreaks.”
The authors noted that other studies showed different results, one in China suggested that only 5% of cases were asymptomatic, and a study in Iceland suggested that 43 out of 100 cases were symptom-free. They added that the sampling used in any study is likely to be a factor in their findings.
