More research is needed to understand the so-called "long COVID" condition and the burden it poses on the health-care system, a science advisory group said in a report Tuesday.

The Ontario COVID-19 Science Advisory Table, a group that provides guidance to the province on the pandemic, said the post-COVID-19 symptoms affect about 10 per cent of those infected and can last from weeks to months.

"There is under-recognition both for the public but also among clinicians of this condition because it is hard to define and quantify and because we don't have a lot of information around it," said Fahad Razak, the lead author of the report.

A conservative estimate suggests about 150,000 Canadians who contract the novel coronavirus experience long COVID-19 symptoms, Razak said. In Ontario, between 57,000 and 78,000 people are affected.

The most common of more than 200 different symptoms include fatigue, shortness of breath, general pain or discomfort, anxiety and depression.

Razak said individuals experiencing such symptoms have difficulty performing daily activities and require increased health-care resources.

"The burden will not only be on the health system, it will also be on other parts of society because a lot of the disabilities are not just about medical care, it's about the fact that individuals can't go back to work, it's that they need a supportive home, it's difficulty with work and family life," he added.

The World Health Organization has reported that approximately one in four individuals who were infected with the virus experience symptoms of long COVID for at least one month. Meanwhile, one in 10 people experience symptoms that last beyond 12 weeks.

The Ontario science advisory group said more research is needed on risk factors for long COVID. Vaccination reduces the chance of developing the post-COVID-19 condition, Razak said.

More than 150,000 people in #Canada experience 'long COVID' symptoms: report #Covid19 #PostCovid

To date, nearly 84.5 per cent of Ontarians over the age of 12 have received one dose of a COVID-19 vaccine and 78.2 per cent have two doses.

Razak said the latest report from the science advisory group looked at data from the earlier waves of the pandemic and did not take variants of the virus -- like Delta and Alpha -- into account.

"We don't have the data yet to know the impact," he said. "The worry is that those variants are clearly more infectious so we're potentially running into a problem where we're going to see even higher rates of the post-COVID condition."

There is limited Canadian data on health-care use patterns for patients with long COVID, including emergency department visits and hospital admissions, the science group said. A pan-Canadian study is currently being done to examine these patterns for long COVID-19 patients.

This report by The Canadian Press was first published Sept. 14, 2021.

This story was produced with the financial assistance of the Facebook and Canadian Press News Fellowship.