A new serology survey that shows less than one per cent of the population was infected with COVID-19 in the first wave of the pandemic is a reason to celebrate the province’s gains, but not to become complacent, says the lead researcher.
B.C. has among the lowest per capita case and death rates in North America, said Danuta M. Skowronski of the B.C. Centre of Disease Control.
Fewer than one in 100 residents in the Lower Mainland were infected during the first wave of the virus, demonstrating that mitigation measures were very effective, she said.
Provincewide, community infection rates were even lower.
“We effectively suppressed the community transmission of this virus in our community,” said Skowronski, who added: “We cannot assume that we’re in the all-clear, because it also means that there is still substantial residual susceptibility in the population.”
The study shows that actual infection rates are about eight times higher than reported cases — “which gives us around 16,000, 17,000 people who may have been infected over the period of the last six months,” said Dr. Bonnie Henry, provincial health officer.
Henry has long said there was more infection in the community than the numbers testing positive would indicate.
The paper by researchers at the B.C. Centre for Disease Control, University of B.C., LifeLabs (the only outpatient community-based lab serving the Lower Mainland) and public-health scientists was posted Tuesday in the online publication medRxiv.
It has yet to be certified by peer review.
The data were gathered anonymously from leftover blood drawn from individuals at diagnostic clinics in the Lower Mainland. The subjects were males and females of different ages, including children.
The blood samples of more than 1,700 people — about 100 people in every 10-year life span — allowed researchers to get a quick and comprehensive snapshot of infection rates in the community, said Skowronski.
The samples were taken over two periods, March 5-13 and May 15-27. The serology test looks for antibodies that take about four to six weeks to develop. May was chosen because it was at least a month after the peak of infections.
The study does not provide insight into whether those who developed antibodies for COVID-19 are now immune to the virus and if so, for how long.
Henry said the study was not designed to research immunity, but public-health experts believe having been infected “probably provides some protection,” so someone exposed a second time might not get it again, or might experience a milder form.
“But we don’t yet know that.”
Based on modelling studies around the world, at least 60 per cent of the population needs to have immunity to protect the rest.
Similar serology studies in Spain showed transmission of about five per cent, while in New York state it was seven per cent.
“So, even though they had that tremendous wave and they had a lot of transmission and a lot of illness and, tragically, a lot of people who died, it’s only a very small proportion of the overall community who was sick from the virus,” said Henry. “So nobody in the world has reached that point of herd immunity.
“What we need to get us to that level is an effective vaccine.”
The study is the first in Canada to report infection rates based on the presence of antibodies — produced to resist the virus — in blood samples. The test protocols were in place from similar testing by the B.C. CDC in 2009 for the influenza H1N1 pandemic.