Study: Most People Infected With Coronavirus During U.K. Lockdown Had No Symptoms When Tested

According to a study by researchers from University College London that was published Thursday in the Clinical Epidemiology journal, coronavirus symptoms appear to be “a poor marker of infection,” at least on the days the subjects of the study were tested.

The study used a representative sample collected by the U.K.’s Office for National Statistics of 36,061 people across the England, Wales and Northern Ireland who were tested between April 26 and June 27—during the U.K.’s strict lockdown—that tracked if they were experiencing any symptoms the day they were tested. 

Of those, 115 people tested positive for coronavirus and only 16 (less than 14%) reported having a fever, cough or losing their ability to taste or smell.

More than three-quarters of people who tested positive were also didn’t experience wider symptoms like shortness of breath and fatigue on the day they tested positive for coronavirus. 

However, it’s possible that many of the people who were asymptomatic upon being tested later developed symptoms—according to the World Health Organization, coronavirus’ average incubation period (or the time between infection and showing symptoms) is between 5 and 6 days, plenty of time for a person to test positive, and as researchers pointed out, to unknowingly infect others.

The UCL researchers said the study shows that more widespread and frequent testing is needed to contain outbreaks—and not just of people who are showing symptoms—especially in places deemed “high-risk” where people live or work closely together, like university housing or factory settings.