B.C. COVID-19 modelling group estimates infections '100-fold' higher than official count

The contents of a COVID-19 antigen rapid test kit are picture in Calgary, Alta., Tuesday, Jan. 4, 2022. THE CANADIAN PRESS/Jeff McIntosh

British Columbia's official count of COVID-19 cases is underestimating the spread of the disease in the province by a factor of 100, according to an independent group of researchers.

The latest report from the BC COVID-19 Modelling Group uses blood sample data from Canadian Blood Services and the national COVID-19 Immunity Task Force to estimate the true rate of transmission in the province.

The CITF's data shows that nearly everyone in B.C. has antibodies to SARS-CoV-2 – the coronavirus that causes COVID-19 – either from vaccination or infection, or both. About 50 per cent of the province has antibodies from infection, according to the CITF. 

The modelling group's report compares that total to the official case count, which is much lower. 

"We know that there's only been about 100,000 reported cases in 2022," said Sarah Otto, a member of the modelling group and a professor of biomathematics at the University of British Columbia.

"To get to 50 per cent of the population infected, that's more like 2.5 million cases in British Columbia, so that shows you that there are a lot more infections happening than the number of reported cases."

Throughout 2022, B.C.'s COVID-19 testing strategy has limited access to lab-based PCR tests, and as home-based rapid antigen tests have become widely available in the province, the demand for lab-based tests has declined.

The B.C. Centre for Disease Control only collects and reports data on PCR test results, however, which has meant a large – and growing – gap between the official case count and the actual number of infections people in the province have suffered.

"We estimate, based on how many people have evidence of a past infection in their bloodstreams, that right now we may be undercounting by as much as 100-fold," she said. "So, if you take a look at the official BA.5 wave, it's not all that high. But magnify it certainly 50-fold, but potentially as high as 100-fold."

Over time, Otto said, the official numbers have been growing less representative of overall coronavirus transmission in the province.

"Fewer and fewer people are actually getting officially tested when they come down with COVID, so, I don't know how much further out of whack this can get, but it's certainly really bad," she said.

Looking at the data released by the BCCDC last week can help illustrate the magnitude of the undercounting.

The centre reported 900 new, lab-confirmed cases, which were detected between July 31 and Aug. 6.

That works out to about 129 new infections per day, or about 2.4 per 100,000 residents.

If the conservative figure Otto cited – that B.C.'s cases are undercounted by 50-fold – is correct, then there were 45,000 new cases during the week in question. That works out to 6,429 new infections per day, or 122 per 100,000 people, a significantly higher concentration.

If the official numbers are off by 100-fold, then the true numbers would be 90,000 new cases for the week, more than 12,800 new cases per day, or approximately 244 per 100,000.

Otto said data on COVID-19 transmission should help people make decisions about their safety, but it's hard to make those decisions if the available data isn't accurate.

"I think it's very important that we be able to make wise decisions about the risks that we take – that we know when to mask, that we know when to limit our indoor social activities," she said. "To make informed decisions, we have to have the information."

Right now, Otto said, people should be masking and avoiding indoor gatherings if they want to avoid getting sick with COVID.

She said the modelling group's latest report shows that the latest wave of infections has peaked in B.C., describing the report as "a lot of good news."

Still, Otto added, the peak happened quite recently, and there's still a lot of COVID circulating in the community, even if the BCCDC's numbers don't show it.