Shut out from COVID-19, influenza appears to be making a comeback in Canada. Why?

Flu infections are increasing in Canada – an unusual trend for this time of year when cases typically are in decline.

Since the beginning of April, detections of influenza have “sharply increased,” the Public Health Agency of Canada (PHAC) said in its latest FluWatch report published April 22.

The report, which documented flu activity between March 13 and April 16, shows all indicators of influenza activity have risen in recent weeks — a time of the year when, historically, average flu cases are declining in the country.

About 1,287 laboratory detections were reported, and a majority of cases with detailed age information were in Canadians under 45 years of age.

“Detections of influenza have sharply increased, from an average of 40 detections a week in March, to 492 detections in the most recent reporting week,” the report reads.

“The threshold for calling the start of a seasonal epidemic in Canada is a five per cent positivity rate. With increasing influenza activity, Canada may reach this threshold in the coming weeks and signal the start of a seasonal influenza epidemic.”

Typically, Canada reaches the start of flu season anywhere from late October to early January, a PHAC spokesperson told Global News. Right now, the positivity rate for influenza is 6.8 per cent, which is within previously seen historical levels at this time of year, they added.

When the COVID-19 pandemic began in 2020, the flu was virtually non-existent in Canada due to protective measures put in place to limit the spread of the novel pathogen.

PHAC recorded 69 influenza detections in the 2020-21 flu season. Normally, around 52,000 cases are detected each year.

So far this reporting season, which PHAC indicates as starting on Aug. 29, 2021, Canada has logged 1,842 influenza cases as of April 16. On average, the country sees 43,627 cases recorded by this time of year.

Canada’s recent increase in flu cases comes from spikes reported in Quebec, the Prairies and the territories, the latest federal respiratory virus detection report shows.

To date this season, Canada has seen 12 laboratory-confirmed flu outbreaks; six were in long-term care facilities, five in facilities categorized as “other” and one in an acute care facility. “Other” facilities can include locations like private personal care homes, correctional facilities, and colleges/universities, the government said.

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There are many potential reasons why flu cases are increasing, PHAC said, and one of them may be related to COVID-19.

“One reason for the increase in cases may be due to the lifting of public health restrictions that were in place for the past two years in Canada and globally,” the spokesperson said.

“This late-season increase in cases is not unique to Canada; since early March, influenza activity has increased in both the United States and parts of Europe.”

When the highly transmissible Omicron COVID-19 variant emerged in late November, Canadians across the country saw a reintroduction of protective measures imposed to curb the spread.

But earlier this year, several jurisdictions unveiled plans to lift those measures depending on how their situations improved, and have acted on them since.

Those restrictions like mask mandates — while imposed to limit COVID-19 activity — controlled the spread of viruses like influenza, said Dr. Susy Hota, an infectious diseases specialist with the University Health Network in Toronto.

“It’s probably why if you ask anecdotally, a large sample of people would say, ‘Yes, it’s been great the last two years. I haven’t had other viruses that I normally would get during the year,’” she said.

“These measures are not specific to one type of pathogen. They would work for other things as well.”

It’s unclear if influenza infections will continue to rise, PHAC said. The flu typically persists above the seasonal threshold until late May, but it is “notoriously hard to predict,” the spokesperson added. The next FluWatch report is scheduled for May 27.

What is clear however is that Canadians will likely experience a summer season with loosened COVID-19 restrictions, and that may spell trouble come fall, said Dr. Gerald Evans, an infectious disease specialist at Queen’s University in Kingston, Ont.

If this coming fall and winter are mostly restriction-free, Canadians could likely see the flu and COVID-19 circulate together, he added.

“This coming winter is going to be incredibly important for us to determine what the future is going to look like with these two viruses circulating around,” Evans said.

“Wear a mask if you are concerned about infections, particularly if you carry personal risk or you live or hang around with people who may be at considerable risk.

“Obviously, when it’s not mandated, it depends on personal preferences, so my message would be really give it some serious thought: wearing a mask is not that onerous, particularly during the winter.”

Canadians should also keep up-to-date with vaccinations, Hota said.

“Whatever we can do to reduce the number of people who are really negatively affected by any of these viruses … the better it’s going to be for all of us to get through the fall and the respiratory virus season, and make sure that hospitals don’t get overwhelmed and we’re not back at that place again,” she said.