Study showing more COVID-19 infections than test rates will guide B.C. response

VICTORIA — A recent study in British Columbia confirms far more people have carried the novel coronavirus than were tested for it, and public health officials say the findings will help tailor future strategies to control the illness.

Provincial health officer Dr. Bonnie Henry and lead author Dr. Danuta Skowronski with the BC Centre for Disease Control say the serology study determined the level of antibodies in hundreds of blood tests.

Tests, gathered anonymously from Metro Vancouver residents whose blood was being checked for unrelated reasons, revealed about eight times more infections than reported cases of COVID-19.

Despite that, both doctors say the rate of community transmission was low at less than one per cent, which they credit to careful observance of physical distancing and other infection control measures.

To date, B.C. has confirmed 3,170 cases of COVID-19, with 21 new cases reported Thursday.

Of those who tested positive, 2,789 have recovered. There have been no new COVID-19 related deaths, for a total of 189 deaths.

Henry says given the scant level of community transmission, what is now needed is targeted testing to determine who has been most affected by the respiratory illness.

She notes the serology study did not include people associated with long-term care homes and further testing would include health workers, some ethnic groups and certain economically vulnerable populations.

Henry told a news conference in Victoria on Thursday serology testing will help determine if transmission has been missed “when cases pop up out of nowhere seemingly.”

She says when an outbreak occurred in Alert Bay off northern Vancouver Island in late April, serology tests were done on “a good proportion” of residents there.

“That gives us a better idea of how this virus is transmitted in community settings so we can more nimbly target outbreaks (elsewhere) as we go into the fall,” she says.

Researchers relied on four measures, or assays, to identify COVID-19 antibodies in the blood of test subjects because no single assay is a completely reliable marker, Skowronski says.

So-called neutralizing antibodies are considered the “gold standard” of contact with a particular virus and Skowronski says such antibodies were found in blood tests analyzed in mid-May.

Henry says researchers are unsure how much protection antibodies may provide to those who have been exposed to the illness, or how long any protection might last. 

“This study does not address that question,” says Skowronski.

“It does, however, very clearly say that we do not have sufficient immunity in the population to prevent subsequent waves.”

That means it will come down to individual and collective measures of British Columbians to continue to keep this virus at bay, Skowronski says.

“We cannot rest on our laurels, we cannot assume we are in the clear, because (the study) also means there is still substantial residual susceptibility in the population.”

— By Beth Leighton in Vancouver.

This report by The Canadian Press was first published July 16, 2020.

The Canadian Press