British Columbia

Fewer than 1% of British Columbians had coronavirus by the time restrictions eased in May: study

A new B.C. study, the first in Canada to report sero-prevalancy, has found a low level of coronavirus antibodies in the population between March and May.

The study, which has not been peer-reviewed, is the first in Canada to report sero-prevalence estimates

A medical lab technician draws a blood sample for a point of care COVID-19 antibody test at the B.C Centre for Disease Control lab in Vancouver, British Columbia on Friday, May 15, 2020. (Ben Nelms/CBC)

A new joint study from the University of British Columbia, the B.C. Centre for Disease Control, LifeLabs and public health scientists has found a low level of coronavirus infections through serology testing, adding to the evidence that British Columbians were able to successfully suppress community virus transmission throughout the early 2020 period.

The study, which has not been peer-reviewed, is the first in Canada to report estimates of coronavirus antibodies in the general population. 

Using sero-prevalence research (looking for antibodies in the blood samples of a random group of people), it estimates fewer than one per cent of British Columbians were infected with coronavirus by the time first wave restrictions were eased in May.

It means around eight times more B.C. residents have been infected than the number of cases reported, the study authors estimate. Fewer than one in 100 people in the Lower Mainland became infected with COVID-19, suggesting an even lower infection rate for other parts of the province.

'We cannot rest on our laurels'

Speaking to reporters on Thursday morning, Dr. Danuta Skowronski with the BCCDC said the infection rates detected were lower than she had anticipated.

"We have great confidence in our findings," she said, adding the results do not reduce the potential for future infections in B.C.

"We cannot rest on our laurels — we cannot assume we are in the all-clear because it also means there is substantial residual susceptibility in the population."

Provincial Health Officer Dr. Bonnie Henry said the rates of infection detected in B.C. remain far too low to allow for immunity protection, but speak to the success of measures taken to curb the spread early in the pandemic.

"We have just minimized the impact of this first wave very effectively," she said.

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Dr. Bonnie Henry says seeing the number of new cases of COVID-19 rise above 20 per day is "way above my comfort zone," but is understandable as the province eases restrictions.

Samples taken from labs in Lower Mainland

The study looked at samples taken in March and May from labs in the Lower Mainland where community cases of coronavirus were expected to be highest.

Researchers screened the samples for antibodies. In March, two out of 869 samples were positive, but neither of them had any antibodies. In May, four out of 885 samples were positive and all four had antibodies. 

The paper noted that there were limitations in their analysis, pointing out that there is uncertainty in how long antibodies remain in the body after a coronavirus infection or whether those who are asymptomatic have them, which may lead to under-estimation of sero-prevalence.

But Skowronski said she believed the results were likely to be more accurate because the blood samples were random and not based on volunteers. Research dependent on voluntary donors tends to skew toward higher infection rates as those people often have reason to be worried they have the virus.

Though the study is the first of its kind in Canada, B.C.'s numbers are low compared to other parts of the world where similar research has been conducted. For example, a similar study conducted in Spain showed 11 per cent prevalence, while another in New York City at one point detected 14 per cent.

Double-edged results

Dr. Srinivas Murthy, an associate professor at the University of British Columbia, was not involved in the study but is a COVID investigator for the World Health Organization.

"I'm heartened by the results in that we're doing a good job, or have done a good job, over the past few months at reducing the community burden of infections," Murthy said. 

However, Murthy noted the results are sort of doubled-edged, as the low presence of antibodies in the population mean more people are vulnerable to any future spikes in coronavirus.

"We think that if you have antibodies, you will not be infected," he said. "If, in fact, there is a low sero-prevalance of protective antibodies against [coronavirus] then that does leave us vulnerable to further infections."

The researchers are in the process of contacting some of the 400,000 British Columbians who volunteered to participate in future serology testing, with the hopes of understanding how the virus affects different socio-economic and ethnic groups.

With files from the Canadian Press, Andrea Ross, Micki Cowan


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