3.5 million Canadian adults have had long COVID symptoms: StatCan study

New data show millions of Canadians have experienced symptoms of long COVID, with some still suffering from debilitating side effects a year or more after being infected.

In some cases, long COVID could be down to a “compromised” immune system, scientists say, which has other people asking whether COVID might be increasing our chances of getting sick with other infections.

About 3.5 million Canadians have experienced fatigue, brain fog, shortness of breath and other lingering symptoms for three months or longer after a confirmed or suspected COVID infection “that could not be explained by anything else,” according to a national study.

As of this past June, more than half — 2.1 million people — were still experiencing symptoms, 11 months, on average, after their last known encounter with SARS-CoV-2.

“As of June 2023, about 100,000 Canadian adults have been unable to return to work or school because of their symptoms,” according to the survey by Statistics Canada and the Public Health Agency of Canada.

The findings fit with Dr. Manali Mukherjee’s personal and professional experience. It took 18 months for the McMaster University immunologist to recover from long COVID.

The problem has been pinned on rogue autoantibodies that turn on the body’s own tissues, attacking the “host,” or overactive cytokines, proteins that boost inflammation as part of the body’s natural immune response. “Cytokines give us an idea that there is still inflammation going on,” Mukherjee said.

The new study is an update to preliminary findings released last summer on the ongoing experiences of COVID in Canadian adults more than three years after the start of the pandemic.

The findings are consistent with other international studies, including a recent study published in Nature Medicine that found increased risks of cardiovascular issues, diabetes, lung problems, gut problems, blood clots and other conditions up to two years later, after even mild or moderate COVID infections.

“A lot of people think, ‘I got COVID, I got over it and I’m fine, and it’s a nothingburger for them. But that’s not everything,” the study’s senior author, Ziyad Al-Aly, a Washington University School of Medicine clinical epidemiologist told the Washington Post. For some people, “it’s still wreaking havoc in your body.”

The Nature Medicine study was based on the health records of U.S. military veterans (most of them men) who were infected before vaccines and drugs like Paxlovid, the antiviral pill used to treat COVID-19, became available.

COVID is known to cause damage to organs and the vascular system in some people. And some doctors have again raised the spectre, recently amplified on social media, that COVID “damages the immune system,” rendering people more susceptible to other respiratory viruses or pathogens, a claim several of Canada’s leading experts in virology and immunology say is speculative rhetoric that exaggerates COVID’s risks.

Like other respiratory bugs, COVID-19 can lead to “temporary perturbation” in the immune system, “but not what can be considered a truly immunocompromised state,” said Mark Loeb, a professor of pathology and molecular medicine at McMaster University.

“It’s not that I don’t believe it is possible that COVID might, in some cases, cause immune deficiency — it’s simply that there is not currently sufficient evidence to conclude that it happens,” Miller said in an email.

“Is getting infected good for you? Of course not. Should we take steps to prevent infection? Absolutely!

“But rhetoric that overstates the current state of evidence related to COVID risks is no more valid than rhetoric that diminishes the seriousness of COVID-19.”

On X, formerly Twitter, Dr. Lisa Iannattone, an assistant professor of dermatology at McGill University, said COVID “immune damage” could be contributing to recent surges in RSV and other respiratory infections.

Iannattone cited a recent study that found a prior COVID infection was associated with a 40 per cent increased risk of an RSV infection needing medical attention in children during the 2021 and 2022 RSV seasons.

Another study this year reported a higher risk of shingles in the 12 months after a COVID infection, while an Israeli team reported a higher risk of streptococcal tonsilitis, among other conditions, a year after a mild case of COVID.

“It’s hard to make any firm conclusions,” Iannattone said in an interview with National Post. “My concern is that at least a subset of people do seem to be having this period, post infection, where their immune system is dysregulated.”

“It’s difficult to understand why we wouldn’t be throwing that in as one of the main hypotheses of things that could be contributing to what we’re seeing,” she said.

Loeb said the early RSV surges “had nothing to do with some sort of global immune dysfunction.” Rather, many children were seeing RSV for the first time, all at once, after being sheltered by lockdowns, physical distancing and other measures during the pandemic’s earlier waves.

It can take weeks to clear all infected cells from the body, said University of Ottawa molecular virologist Marc-André Langlois. Some cells might also contain bits of the viral genome that can trigger inflammation.

“As it stands, I would be cautious to make claims that these observations are unique to COVID, and I would at this time avoid using words such as ‘immune threat’ or ‘immune dysfunction’ until there is more evidence,” Langlois said in an email.

A subset of people with long COVID do appear to have immune systems that are “a little compromised,” leading to that malaise and fatigue, Mukherjee said.

While most symptoms clear within a year, “We’re still dealing with the aftermath of COVID,” she said.

About one in nine of all Canadian adults have experienced long-term symptoms from a COVID infection, reported the StatCan study.

Some people still question just how debilitating long COVID can be, or whether it’s a true phenomenon, said Mukherjee, who struggled with staggering fatigue, sudden plummeting blood pressure and phantosmia, where people smell “phantom” odours that aren’t there.

“I’ve been pacing myself,” she said. “That’s helped me not have a relapse, thus far.”