Wastewater and Denmark: Here's what experts are looking at to know if B.C. is turning the corner on Omicron

At the B.C. government's pandemic press conference on Tuesday, provincial health officer Dr. Bonnie Henry said "we know this wave will move through quickly."

But when asked to clarify how the province could be so certain, Henry backtracked.

"If I sounded like I was sure about that, then that was my mistake," she said.

Henry then talked about how the number of COVID-19 cases have begun going down in the United Kingdom and levelling off in other jurisdictions with an Omicron wave that began at a similar time to British Columbia.

"We tend to see this with any pathogen that has a shorter incubation period. You see this rapidly explosive growth, and you see a rapid decrease once a certain level has been reached in the population."

The comments reflect some of the ongoing scientific discussion around Omicron's path: a lot of theoretical confidence, and a thesis that still needs to be played out.

A rapid fall

The independent B.C. COVID-19 Modelling Group, which consists of researchers from several universities, has differed from the provincial government's projections on several occasions.

But one of its members, University of British Columbia professor Dr. Sally Otto, said she, too, expects a rapid fall on the number of COVID-19 cases after the current rise.  

"We know that in epidemiological principles in general, a disease that spreads more rapidly through a population runs out more quickly of individuals that are susceptible to it," she said, adding she believes B.C.'s numbers will begin declining by the end of January. 

"It would be a real surprise not in keeping with our understanding of COVID that we don't build up an immunity to Omicron."

Similarly, Otto said the steepness of B.C.'s decline will be based in part on how quickly transmission has occurred. 

"Bending down the curve can keep the peak kind of indefinitely long if you bend it down before it reaches the peak, and it just kind of putters on," she said. 

"But honestly, I think that the measures that we have in place are not substantially bending down that curve." 

Testing wastewater

Many provinces have seen similar rapid upward curves, with similar health measures in place and similar limitations on testing. 

This means pandemic observers from coast to coast are all looking at similar metrics — from rates of transmission in jurisdictions further along the curve, like Denmark and the United Kingdom, to new hospitalizations each day, to the amount of viral particles in your toilet.

"What we have to go on instead is wastewater testing," said Raywat Deonandan, epidemiologist and associate professor at the University of Ottawa. 

Measuring the viral load of COVID-19 in wastewater plants has been used in many places as a leading indicator of where the virus is heading, since it can track transmission before people feel the need to get tested. 

But it's not without issues, said Deonandan, because of questions around the potentially smaller viral load of Omicron relative to other variants.

He also cautioned that different transmission rates will lead to different hospitalization numbers, depending on provincial factors like overall vaccine rates and the health of the population.

"We can't disentangle the fact that a high number of cases doesn't necessarily equate to an overburdened hospitalization system," he said. 

B.C. has only begun reporting viral wastewater loads in Metro Vancouver on a daily basis. The number of new daily hospitalizations is now around 60, and has not yet gone down.  

"How [this] will play out in hospitalizations, and the length of time that we're going to see hospitals being strained is also something we don't yet know," said Henry.