At least 1 in 3 COVID-19 infections are asymptomatic, study suggests

People wear face masks as they walk along a street in Montreal, Saturday, January 23, 2021, as the COVID-19 pandemic continues in Canada and around the world. THE CANADIAN PRESS/Graham Hughes

TORONTO — A review of 61 studies and reports comprising more than 1.8 million people suggests that at least one in three people infected with COVID-19 do not have any symptoms, according to a study published in the Annals of Internal Medicine.

Authors from Scripps Research in San Diego, California, reviewed global studies and reports published through Nov. 17, 2020 – including two large surveys in England and Spain – that tested the presence of COVID-19 antibodies in over one million people.

The researchers compiled 43 studies that used PCR testing and 18 studies that used antibody testing to cross reference their data.

The compiled data showed at least one-third of individuals tested positive for the virus but never experienced symptoms.

Data like this highlights the importance of testing asymptomatic people, said Medical Director of the Vancouver Infectious Diseases Centre Dr. Brian Conway, on CTV’s News Channel Saturday.

“If we identify groups of individuals for whom the transmission network is unclear, I think there is a role for testing larger numbers of asymptomatic individuals to… interrupt those transmission networks more effectively,” Conway said.

It is a sentiment echoed in the study.

“In light of the data presented here we believe that COVID-19 control strategies must be altered, taking into account the prevalence and transmission risk of asymptomatic SARS-CoV-2 infection,” the study notes, adding that as vaccines roll out globally, “more research will be needed to determine their efficacy in preventing asymptomatic infection.”