British Columbia will stop screening all positive COVID-19 tests for variants of concern, with medical experts saying the practice becomes less meaningful as variants drive case counts during the third wave of the pandemic, and one of them is poised to become the dominant source of infections in the province.
B.C. is now developing a strategy that will limit screening for variants largely to surveillance testing, which involves a sampling of the population, and will focus on health measures to prevent deaths and serious illness. It is expected to be implemented in coming weeks.
Mel Krajden, medical director of the BC Centre for Disease Control Public Health Laboratory, said it is unrealistic to stop the virus from spreading without “draconian” restrictions, and that efforts should instead be focused on protecting the population from their most serious harms.
“For us to believe that we are going to contain this by doing an additional test to say whether it’s a variant or not a variant is not realistic. It’s a false premise, in my mind,” he said.
“The important question is how well you are protected from these variants. And the best way to know that is … to do unbiased surveillance on what are the strains circulating in B.C. and how they are changing over time.”
Dr. Krajden said the province will still do whole genome sequencing for cluster identification, for travellers and to identify the source of infection in certain outbreaks.
“But when you do it in a random way [with surveillance testing], you’re really trying to sample to say, ‘Okay, what is circulating this week versus what circulated last week? Where are the hot spots? How do you support people? How do you vaccinate people quickly?’”
As of Wednesday, the province had confirmed a total of 3,766 COVID-19 cases that are variants of concern: 2,837 of the B.1.1.7 variant first detected in Britain, 878 cases of the P.1 variant first detected in Brazil and 51 cases of the B.1.351 variant first detected in South Africa. Of all variant cases, 266 are confirmed active, however this reported figure lags behind actual active cases. The B.1.1.7 variant is expected to become dominant in coming weeks.
Caroline Colijn, a mathematics professor and Canada Research Chair at Simon Fraser University, said the shift is logical given the limited sequencing capacity but that there are numerous advantages of screening all positive cases.
“If the question is: ‘Is it B.1.1.7?’ we know it’s likely going to be B.1.1.7 and we may not need to do sequencing 95 per cent of the time to [confirm] that,” she said.
“But if the question is: Where is our COVID coming from? What is the role of international borders? What is the role of interprovincial travel? Are we seeing introductions of other COVID? Those are all some of the roles of sequencing.”
Dr. Colijn said the shift will also necessitate reporting transparently not only on the number of variants detected but the number of tests screened.
“If they don’t say how many they tested or when they were from, then it’s like reading tea leaves,” she said.
Catalina Lopez-Correa, executive director of the Canadian COVID Genomics Network, said the collaboration for sequencing is working on an updated sampling strategy to ensure provinces properly align their sequencing efforts.
“Some regions are now doing more surveillance testing to get a better idea of the spread of these variants but we continue also to prioritize samples that we think are suspicious of having one of the variants of concern,” she said in an e-mail.
“SARS-CoV-2 Genome sequencing continues to be the gold standard to fully confirm the presence and evolution of the variants.”
On Tuesday, Provincial Health Officer Bonnie Henry spoke of “a whole landscape of these different viruses and different variants” that officials were monitoring, including the P.1 variant most commonly associated with Brazil.
Dr. Henry said it was likely that it was introduced to B.C. by visitors from other parts of Canada and then began circulating through several chains of transmission in the province. A “high percentage” is associated with Whistler, she said, where many visitors and staff members of the Whistler-Blackcomb ski resort have contracted the disease.
As of Tuesday, 197 cases of the P.1 variant were detected in Whistler, which had a total of 1,120 COVID-19 cases from Jan. 1 to March 28.
Dr. Henry said officials are monitoring whether the increasing prevalence of variants will have any impact on vaccine effectiveness and, to date, have not seen any notable impact.
The Provincial Health Officer also alluded to the upcoming shift in testing strategy.
“We need to use our surveillance resources – because we have a limited capacity to do whole genome sequencing – to focus on making sure we can detect if any other new variants that have some different mutation arise in the province as well,” she said. “That is part of what we will be focusing on in the coming weeks.”
With a report from Ivan Semeniuk
We have a weekly Western Canada newsletter written by our B.C. and Alberta bureau chiefs, providing a comprehensive package of the news you need to know about the region and its place in the issues facing Canada. Sign up today.