Health Minister Adrian Dix and Chief Provincial Health Officer Dr. Bonnie Henry provide an update on COVID-19 on December 21, 2021. Province of BC / Flickr

What does BC’s daily COVID case rate mean now? Very little, says modelling expert

Dr Sarah Otto said the province needs more information about the newly arrived fourth wave—but with testing capacity reached, there’s less data to get it from.

By Srushti Gangdev | December 29, 2021 |2:57 pm

BC’s move to reserve COVID testing capacity means that the province will no longer have an accurate idea of its case rate, or the path of the pandemic’s fourth wave, says an independent modelling scientist.

In a Christmas Eve press conference, provincial health officer Dr Bonnie Henry told reporters that daily testing capacity has essentially been maxed out in BC, and public health needed to save its PCR tests for people most at risk.

Health authorities, including Fraser Health, are now telling British Columbians that they don’t need to get a COVID test even with symptoms if they are fully vaccinated and able to manage their symptoms by themselves.

Evolutionary biologist and member of the BC COVID-19 Modelling Group, Dr. Sarah Otto, told the Beacon that means we don’t have an accurate idea of how many people are actually being infected in the province each day.

“Young people and people without medium to severe symptoms are being requested not to use the PCR tests—that’s one [reason]. [During] the holidays, people don’t want to go out and spend hours in a line. And then, of course, it was freezing cold, and a couple of the centers were closed. So we don’t even have information from those particular centers,” she said.

That means that the province’s daily case rate—which accounts for positive PCR test results only—should be taken with a grain of salt.

On Tuesday, for instance, BC reported 1,785 new cases (no new information on hospitalizations or testing rates was provided). That’s a far cry below the record-setting numbers in the mid-2000s we had in the days leading up to Christmas.

“We would predict from the models about 4000 cases today, if the reporting standards hadn’t changed and if people’s contact rates hadn’t changed. But we don’t know,” Otto said.

“Of course, the restrictions may have led to fewer infections. But the holidays may have led to more infections. So it’s challenging to know.”

Correcting the case rates

Otto said the province needs more information about the newly arrived fourth wave—but with testing capacity reached, there’s less data to get it from. One way to correct the case rate would be to track wastewater samples, which can help show the prevalence of COVID-19 in the general community. Metro Vancouver tests wastewater samples for COVID-19 every three days, but it hasn’t updated its data on its website since Dec. 19.

Normally, we would be able to correct our case rate based on extrapolating hospitalization levels—but that would only work if we knew what proportion of people sick with a particular variant end up in hospital. And while the Omicron variant has become dominant in a very short time, it’s still new enough that we don’t accurately know its hospitalization rate.

That means that not only can we not correct the case rates, but the rationing of PCR tests means our ability to figure out how severe Omicron is for our population has been stunted.

Why does it matter to have an accurate idea of the daily case rate? There’s a few reasons, Otto said.

“Because if there’s 30,000 cases versus 3000 cases, that changes the calculus of what are safe spaces and how much risk to take. So the real numbers do matter for individual decision-making. And then they really matter for projections,” she told the Beacon.

“If there are a lot of infections [now], then we’ll hit the peak and be on the other side of the Omicron wave sooner. But predicting when that peak will happen is impossible if you don’t have accurate numbers of cases. And finally, there still is a lot of uncertainty about hospitalization rates. But in order to predict those hospitalization rates, we need accurate estimates of cases.”

Another way to fill the gap in PCR testing capacity, Otto said, would be to make rapid tests widely accessible to British Columbians. This is something that she’s called for in the past as well.

She said with PCR testing capacity throttled and little access to rapid tests, people with mild symptoms may make the decision to not get tested at all—and go about their days, possibly exposing many more people to the virus.

“A really important thing to emphasize is that the symptom spectrum has changed with Omicron. Loss of smell is not so common, the lower lung congestion is less common—it’s more head cold [symptoms],” Otto said.

“And so it’s very easily dismissed as just a cold when it’s Omicron. So for that reason, people are much more likely to ignore their symptoms and go about their daily life unless they have easy and fast access to testing, like with rapid antigen tests.”

BC’s access to rapid tests

While provinces like Nova Scotia and Ontario have made rapid tests widely available to residents for free, public health officials in BC have given a wide range of reasons why those models wouldn’t work here.

Earlier this month, for instance, Henry told reporters that the federal government had sent BC “different” rapid tests than the other provinces that were not designed for at-home use.

She then clarified that BC had actually received some 700,000 rapid tests that can be self-administered, but said that they were sent in bulk packages that presented a logistical challenge in sending them out individually.

Nova Scotia got around that problem in September, by having volunteers separate out the tests into individual packaging.

And while Henry has also said that rapid tests are less effective than PCR tests in detecting illness, the province has pointed to a supply shortage in rapid tests. It plans to expand its rapid testing program in the new year, when it receives new shipments from the federal government.

But it’s important to note that the province is responsible for informing the federal government of how many tests it actually needs. And as for the type of tests it receives—it’s involved in those conversations as well.

“Provinces and territories provide Health Canada with their rapid test quantity requirements. Health Canada, in partnership with the provinces and territories, jointly agree on which type of tests they would receive, how many, and when, depending on the type of testing program they want to implement and the supply capacity of the manufacturers at a given time,” the Public Health Agency of Canada told the Beacon in an emailed statement.

Otto agreed that rapid tests may not pick up a positive result from someone infected with Omicron at the beginning of their infection—but said in the absence of easily accessible PCR testing for all, making sure everyone has access to multiple rapid tests would be helpful in catching infections.

She said people who knew they were exposed to the virus would be able to test every day to confirm whether they had been infected. And while those tests are available on the free market, she pointed out that they are “prohibitively” expensive for many people.

Srushti Gangdev

Reporter at Burnaby Beacon

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