A new study has found that less than one per cent of British Columbians had been infected by COVID-19 by late May, public health officials said Thursday.
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The serology study tested blood samples for traces of four virus-related antibodies and found about 0.55 per cent were positive.
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That suggests about 16,500 people have contracted the virus in the province.
The results from the study, the first of its kind in Canada, warrant “a big bravo to British Columbians,” researchers say.
“We successfully suppressed the spread of this virus in our communities,” said Dr. Danuta Skowronski, the study’s lead author and epidemiology lead of influenza and emerging respiratory pathogens at the BC Centre for Disease Control.
The number of estimated infections based on the study is about eight times higher than the number of reported cases at the time the samples were taken between March and May.
That’s likely because of limited testing in the early days of the province’s outbreak, officials said.
“We know there was a period of time where we were not testing everybody,” said provincial health officer Dr. Bonnie Henry. “There are more people that have this infection in our community than people who have had a test.”
However, similar studies from other jurisdictions reported 10 to 12 times the number of infections compared to reported cases.
B.C. is “amongst the lowest per cent for infection and death rates not only in Canada, but in North America,” said Skowronski.
But the low rate of infection revealed by the study’s initial results mean the population remains vulnerable to a resurgence in a likely second wave of infections.
“We don’t have sufficient immunity to stop a second wave,” said Henry. “We have a long way to go before we’re there, which means it really comes down to the individual and collective actions of British Columbians.”
Protocols developed to trace infection during the H1N1 epidemic in 2009 were activated to quickly begin serology testing for COVID-19, Henry said.
One thousand anonymous blood samples from individuals of all ages undergoing diagnostic tests for other conditions in the Lower Mainland were tested for signs of four antibodies related to COVID-19.
At least two of the four indicators had to be present to be considered a positive test.
But antibodies are not developed until up to six weeks after infection and little is known about short or long-term immunity to COVID-19, meaning the study doesn’t necessarily indicate the trajectory of the province’s outbreak.
The information will help guide targeted testing of certain groups, like health-care workers, who are at higher risk of becoming infected.
“Randomly testing asymptomatic people in B.C…. would be a waste of resources, frankly,” said Henry. “The serology survey supports that this is a smart strategy for us right now.”