Omicron arrived a month ago. When will hospitals see a rise in cases?

It's been a month since Canada's first COVID-19 case involving the Omicron variantwas confirmed in Ottawaand while local case numbers have since shot up, hospitalizations remain relatively stable.

So what's going on? Shouldn't patientshave already started showing up athospitals and emergency rooms? Is it a sign this latest wave will be less severe?

Not necessarily, say some infectious disease experts and the reason likely has to do with demographics.

As of Thursday,Ottawa was reporting almost 2,800 known active COVID-19 cases. Only 104 cases in the city have been confirmed to involve Omicron, althoughsome 718additional cases are likely due to the highly transmissible variant.

That transmissible nature has led to warnings from people like Dr. Theresa Tam, Canada's chief public health officer, that people must reduce contacts or the country'shospitals will be overrun.

"Even if Omicron happens to be milder than the previous virus variants, because it's spreading so rapidly ...even a small proportion of people winding up in hospital is going to overwhelm our systems," Tam told CBC'sThe Nationalthis week.

• Reduce contacts now or hospitals will be overwhelmed by Omicron, says Tam

In Ottawa, that hasn't yet happened: as of Wednesday Ottawa Public Health was reportingsix residents being treated for COVID-19 in a city hospital. The number'sbeen in the single digits since Dec. 3.

In the Kingston, Ont., area, where Omicronwas also circulating in late November, there were 24 people in hospital with COVID-19 as of Tuesday higher than in Ottawa, but also the lowest number in that region since Dec. 6. And it's a similar story in other eastern Ontario health units.

But what's going on now also occurredwhen Alpha and Delta arrived on the scene: initial cases are circulating among younger, healthier people with stronger immune systems, said Dr. Gerald Evans, an infectious disease specialist at the Kingston Health Sciences Centre and Queen's University in Kingston.

'The first vanguard'

Over the first three weeks of December, roughly 90 per cent of the cases in the hard-hit Kingston area were inpeople ages18 to 39, Evans said.

It's a demographic that's more likely to go out to bars, restaurants and other venues where mask-wearing and physical distancing might not be observed so closely, Evans said.

That's why, over the course of the pandemic, they've been "thefirst vanguard of the virus."

"It is quite possible that the lack of hospitalization just represents a demographic [where you would] have expected a very infrequent number of hospitalizations," said Evans. "That's why that signal hasn't popped up yet."

It's a view shared by Dr. Doug Manuel, a senior scientist with The Ottawa Hospital who tracks local COVID-19 numbers.

New waves typically start in younger folks before spreading out to other groups, Manuel told CBC in an email. Omicron-related hospitalizations will start to show up when middle-aged, older and unvaccinated Canadiansstart to be infected in larger numbers, he said.

In the third wave, for example, Ottawa hit its record number of COVID-19 patients in hospital, 125,one week after its highest one-day report in cases.

For now at least, cases in Ottawa remain highest among younger residents who are "very unlikely to be hospitalized," said Dr. Vera Etches, the city's medical officer of health, at a Wednesday press conference.

"It doesn't take longespecially with Omicron, and especially if people aren't being careful with gatherings over the holidays between generations [for this to]reach the population at greater risk of hospitalization," she said.

Wastewater signal murky

Despite those well-established trends, Omicron also contains unknowns particularly the fact it seems tobe "expressing itself differently" in Ottawa's wastewater,said TysonGraber, associate scientist with CHEO and co-lead investigator with the city's wastewater monitoring project.

It took roughly aweek for Omicron to displace Delta as the dominant variant in the wastewater signal, Graber told CBC Radio'sOttawa Morning significantly faster than both Alpha and Delta.

But what's peculiar, he added, is that as Omicron has gained a hold, the overall viral signal in the wastewater has actually dropped.

That could be because infected people shed less virus when they're infected by Omicron,Graber said, or because high immunization rates mean not as much of the virus ends up in the wastewater although both hypotheses remain"pure speculation."

• Omicron is blurring true picture of COVID-19 cases. But experts say there are other ways to capture it

What it does suggest, he added, is the pandemic has once again entered a curious newstage, although whether it's a less severe one remains to be seen.

"We can hope, especially at this time of year. But we can't put everything into hope. And we have to be prudent," Graber said. "We know what happened in the past, and we don't want that to repeat itself."

To avoid history from repeating itself, Canadian jurisdictions should think hard about following in the footsteps of Quebec and Ontario and reintroducing tough COVID-19 restrictions, Evans said.

Ultimately,eastern Ontario's experience with Omicron will be more valuable for Canadian health unitsthan what's going on in places like South Africa or the United Kingdom, he added, where thehealth systems vary widely.

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"Seeing what's happened here in Kingston, seeing what's happening here in Ontario and Quebec, [it's] probably a good harbinger for the rest of the country," he said.

"We know Omicron is really across the country at the moment ... it's just going to continue to grow."