Open this photo in gallery A nurse greets patients outside a coronavirus disease (COVID-19) assessment center in Ottawa, Ontario, Canada March 25, 2020. PATRICK DOYLE/Reuters

The Public Health Agency of Canada says roughly one in 10 hospitalized cases of COVID-19 is a patient under 40-years-old.

The agency confirmed the figure late Saturday night, correcting information released earlier in the day by Canada’s Chief Public Health Officer Dr. Theresa Tam.

“Based on a subset of case reports with age and hospitalization data, 12 per cent (not 30 per cent) of those hospitalized were under 40 years of age,” spokesman Eric Morrissette said in an e-mail.

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The lower number is much closer to the 11 per cent hospitalization figure for that age group released in an epidemiological report of COVID-19 that the agency released early Saturday.

Experts caution though that the lower figure is still significant and confirms that young adults need to take the disease seriously. The hospitalization for younger generations shows that they are getting “really, really sick,” said Matthew Miller, an associate professor at McMaster University’s Michael G. DeGroote Institute for Infectious Disease Research.

“I’m a pandemic flu expert and this is not the flu,” he said, “This is very different, it’s certainly worse for young adults than the flu.”

Epidemiological data released by the Public Health Agency of Canada gives a first glance at the severity across the country and confirms the vast majority of new cases are due to community spread. It also highlights an ongoing gap in the data available.

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The government released the report on Saturday morning, it is based on numbers as of 10 a.m. E.T. on Friday. At an Ottawa press conference at noon local time, Dr. Tam released figures that differed from the statistics outlined in the report.

The report also showed that 13 per cent of confirmed COVID-19 cases result in hospitalization, while Dr. Tam used a lower figure, saying the hospitalization rate was seven per cent. The public health agency said the discrepancy is due to two different sets of data. “The 7 per cent hospitalization rate was based on real time data reported publicly by provinces,” Mr. Morrissette said.

The agency also receives detailed case reports from the provinces and territories, he said, those case report forms “lag behind the real time data, while they provide more in depth information for epidemiological analysis.”

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Epidemiologists say the data released in the report are significant but also caution that the lag in getting the information means it doesn’t depict what’s happening now, but rather what’s already occurred.

According to Dr. Tam:

There are 5,153 confirmed cases of COVID-19 and 55 people have died as a result of the disease in Canada

Approximately seven per cent of people with COVID-19 require hospitalization; three per cent become critically ill; and one per cent of cases are fatal.

According to the report:

People over the age of 60 have the highest rate of hospitalizations making up 56 per cent of hospital admissions and 52 per cent of people needing intensive care.

Individuals aged 40-59 had the highest proportion of cases (34 per cent), followed by those 20-39 years of age (28 per cent) and 60-79 years of age (23 per cent).

88 per cent of new cases identified this past week are from community transmission rather than travellers arriving from abroad.

62 per cent of the documented cases included enough information for the public health agency to include them in the epidemiological summary; only 35 per cent of the reported cases included information on the rate of hospitalization.

At a press conference in Ottawa on Saturday, Dr. Tam said the data show “we’re definitely not out of the woods” and Canada needs to “double down” on social-distancing measures to stop the spread of the novel coronavirus, which causes COVID-19.

While older generations experience the “heaviest impacts” from the virus, Dr. Tam stressed that younger adults are not immune from severe symptoms.

Tracking the number of hospitalizations is “imperative” to understanding the severity of the disease, Prof. Miller said. He said it’s particularly important given the limitations around testing which makes the total number of COVID-19 cases a “less reliable metric” than the change in hospitalizations and deaths over time.

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However, not all hospitalizations are reported.

According to the report, only 1,413 cases out of the 2,517 included in the overall study included information on hospitalization. Out of 1,413 cases, 188 people were admitted to hospital, 35 per cent of them needed to go into intensive care and 18 per cent required mechanical ventilation.

Ontario is one of the provinces that doesn’t release the number of hospitalizations. However, on Saturday it did report on the most severe cases. Sixty-three patients with lab-confirmed cases of COVID-19 are in intensive-care beds, 46 of them on ventilators, Dr. Barbara Yaffe, the province’s associate medical officer of health, said.

Prof. Miller said the 13 per cent hospitalization rate, identified in the federal report, is in line with what other countries are experiencing. And the number of deaths and ICU admissions are on the “absolute low end” of what the U.S. is seeing.

Open this photo in gallery A man walks through a VIA Rail concourse area at Toronto's Union Station, Saturday, March 28, 2020. Chris Young/The Canadian Press

The report highlights that COVID-19 is not something that should be taken lightly by young adults or middle-aged people, Prof. Miller said.

“Even if there aren’t a lot of young adults who are dying necessarily, there are a lot of young adults who are becoming severely ill,” he said.

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The total number of cases in Canada has been doubling every three days, according to the summary released by the public health agency. However, Dr. Tam said there are signs of hope based on modelling done in B.C. that the social-distancing measures put in place are limiting the spread of the illness.

Dr. David Fisman, a physician at Toronto Western Hospital and professor at the University of Toronto, cautioned that the data doesn’t show what’s happening now but instead what’s already happened.

“There’s a lot of lags, so all of this is really archaeology, you’re looking backwards in time,” Dr. Fisman said. “The problem with that of course is that that means you’re underestimating what’s happening today.”

“You’re not aware that the situation is getting dire, until it’s already dire,” he said.

He said problems with testing in Canada, and especially in Ontario, means experts are starting to understand the size of the epidemic based on ICU admissions and deaths, which are called lagging indicators. Dr. Fisman said those signify transmissions that happened three or four weeks ago, so in late February or early March.

With a report from Kelly Grant, in Toronto.

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How many coronavirus cases are there in Canada, by province, and worldwide? The Globe and Mail has created a tracker where you can check in throughout the days to see latest maps and charts on cases, recoveries and fatalities.