TORONTO -- An antiviral medication originally used to help treat Ebola has been approved by Health Canada for treatment of COVID-19.

Health Canada announced Tuesday that the drug remdesivir has been authorized for treatment of the novel coronavirus in patients with severe symptoms such as pneumonia, or those who require extra oxygen to breathe.

Remdesivir is the first drug that has been approved for treatment of COVID-19 in Canada. The drug has also been granted emergency or conditional authorization in the United States, Europe, Japan, Singapore and Australia.

"This is a medication that works to inhibit the virus itself; many of the other therapeutics we've seen used or attempted for use in the treatment of COVID related disease have been around the immune system," infectious disease expert Dr. Lisa Barrett of Dalhousie University in Halifax explained to CTV News Channel.

"However, this one is designed to directly inhibit the virus itself, and has been used or tested for use in other viral infections previously."

According to Health Canada, remdesivir is recommended for use in Canadians aged 12 years and older who have severe COVID-19 symptoms and weigh of at least 40 kilograms. Health Canada said remdesivir is to be administered through an IV and will be used only in healthcare facilities where patients can be closely monitored

"[It's] definitely not for everyone. This is a medication that's administered through an intravenous, it is meant to be used in people who have severe symptoms and… those will be folks who are going to be in the hospital, who will require hospitalization. Therefore, it really, really is at this point for people who have more severe symptoms," Barrett said.

Health Canada said it completed an expedited six-week review of remdesivir and determined that the drug's benefits outweigh its risks when used against symptoms of COVID-19.

However, Health Canada said authorization of the drug, which is manufactured by Gilead Sciences Canada Inc., comes with some conditions to ensure its "continued safety, efficacy and quality."

Gilead Sciences Canada is required to submit to Health Canada reports on all adverse reactions to the drug, pregnancy safety reports, final data from clinical trials and any foreign regulatory actions related to the safety of remdesivir.

"[Remdesivir] does seem to provide some benefit in the treatment of people with severe symptoms, enough so that Health Canada has decided to approve it with the condition that as the company, and as clinicians and physicians gather more data on it, that they report it to Health Canada," Barrett said.

While remdesivir has been authorized for use, Canada's chief public health officer Dr. Theresa Tam told a press conference on Tuesday that there are still unknowns about the drug.

"The approval is accelerated in collaboration with getting data from other countries and their regulatory authorities and whatever data is available. There'll be ongoing monitoring of the drug in terms of its effectiveness and safety as well," Tam explained.

"It's not something that people can just sort of go out and access by themselves or even hospitals, it would be difficult."

Results released in May from a major study in the U.S. suggested that remdesivir could shorten COVID-19 recovery time.

The U.S. National Institutes of Health (NIH) tested the antiviral medication on 1,063 COVID-19 patients sick enough to be hospitalized.

Officials said recovery in patients using the drug was shortened by 31 per cent -- 11 days on average versus 15 days for those just given usual care.

"It was a well done study, well designed, and it seemed to improve the time people had between when they had bad symptoms, until they felt better," Barrett said, adding that remdesivir is "not an overall cure in one step."

A small number of Canadians have been or are currently being treated with remdesivir under the Special Access Program. With authorization of the drug, the Special Access Program will no longer be required to access remdesivir.

Health Canada said it will continue to closely monitor the safety of remdesivir and will take action should any safety concerns arise. There is currently no expiry on the drug’s approval.

"The Public Health Agency of Canada is continuing to lead work with Gilead Sciences Canada, Inc. to secure access to remdesivir for Canadians," Health Canada said in a statement.

Two existing clinical trials authorized by Health Canada to evaluate the safety and effectiveness of remdesivir are ongoing, according to the health agency.

Tam said she is not aware of the results of the clinical trials, but said researchers are monitoring the drug for certain side effects.

"I do believe that some of the range of side effects could involve other organs such as the liver and others. Health Canada has actually reviewed all this information and determined that the benefits outweigh the risk of the side effects but again, this is not a drug you use as an outpatient. You have to be in a hospital setting where someone can monitor that," Tam said.

Without knowing the drug's side effects, Tam stressed that patients taking remdesivir must be supervised by doctors.

"If you are seriously ill from COVID-19 you may actually have compromised your multiple organ systems and how you metabolize drugs so that's why I think this this drug should be used under those context of close monitoring," Tam said.

Despite authorization, Tam said there are concerns about the supply and cost of remdesivir in Canada.

"Quite frankly, the supply is very limited globally from this company," Tam said, adding that the Public Health Agency of Canada (PHAC) is in talks with the drug's manufacturer.

"I think the company will begin to accelerate its capacity but the bottom line is that the supply is not plentiful. So we will do what we can to get some of the supply for Canada."

In regards to cost, Tam said remdesivir will "undergo the appropriate reviews in terms of the pricing" but did not provide a specific dollar amount.

"I am aware that some of these medications or drugs are going to cost a fair amount of money but I think in the negotiation processes you have to sort of look at access as well as what's the reasonable price. All of that will be taken into account," she said.

While approval of remdesivir as a treatment will help in the battle against COVID-19, Barrett warned that more research is still needed.

"Until we have more information, it's a great idea that Health Canada has gotten us access to this tool in our COVID toolbox, but it certainly isn't the end of the story, and we're not certain where it's best used yet," Barrett said.