LONDON — A British study has found 86% of people infected with the coronavirus didn’t show the main symptoms on the day they were tested.

Researchers at University College London looked at data from a survey that has been testing thousands of U.K. households every week, regardless of whether the subjects had symptoms.

The study, released Thursday, looked at data for 36,061 people between April and June. Researchers found among those who tested positive, 86% didn’t have a cough, fever or loss of taste or smell.

Lead researcher Irene Petersen says while people may have had symptoms in the days before their test or developed them later, the study suggests many may be spreading the virus while asymptomatic. She says frequent and widespread testing of all individuals is needed to curb “silent transmission.”