OTTAWA -- Federal agencies are trying to get a handle on how many Canadians may be suffering from long COVID as researchers learn more about the mysterious after-effects of the virus.

The Public Health Agency of Canada and Statistics Canada have launched a survey to try to get a broad idea of how common it is for people to feel lingering effects after COVID-19 infection, which can be difficult to identify and even harder to track.

鈥淲e probably anticipate that the impact of long COVID is going to be quite substantial,鈥� chief public health officer Dr. Theresa Tam said at a media briefing Friday.

Relatively little is known about the effects of long COVID, also known as post-COVID-19 condition, including how to diagnose it, how long it lasts or how best to treat it.

It can affect people who were hit hard by their initial COVID-19 symptoms, but it's also been noted in people who had hardly any COVID-19 symptoms at all.

The public health agency says there have been reports of more than 100 potential symptoms associated with the condition.

The most common ones, according to PHAC, include fatigue, memory problems, anxiety, depression and even post-traumatic stress disorder.

The wide array of symptoms, coupled with the fact that few jurisdictions provide documented COVID-19 tests, make it difficult to know how many people are still suffering the effects of an infection.

Early indications from the World Health Organization showed 10 to 20 per cent of people infected with the virus would go on to have symptoms of long COVID. Tam said more up-to-date research indicates it could actually be as high as 50 per cent.

鈥淟ong COVID symptoms can be quite broad and non-specific, and so depending on the questions and the questionnaire, you might elicit different answers,鈥� Tam said of the complexity of nailing down long COVID cases.

The survey will hopefully give public health officials a broad understanding of how many people are dealing with long COVID and could even help nail down whether certain geographic areas or segments of the population are being hit harder, she said.

The federal government will also look at information gathered from provincial health systems as well as clinics that have been established to specifically deal with long COVID cases.

Tam said there's emerging evidence that COVID-19 vaccines offer some protection against long COVID, but those studies are still ongoing, and the best way to avoid long-COVID is to avoid catching COVID-19 altogether.

The number of new cases appears to be trending down, Tam said, though the number of people hospitalized with COVID-19 remains high in some parts of the country.

The federal government dedicated $20 million over the next five years in its latest budget to support research into the long-term effects of COVID-19 infections, as well as wider impacts of the virus on health and health-care systems.

One of the things researchers are looking for is a better way to diagnose the nebulous condition.

Tam said the survey may give public health officials a better understanding of antibody data, which may even lead to better diagnostic tools for past COVID-19 infection and long COVID.

This report by The Canadian Press was first published May 6, 2022.