Health Canada has approved Pfizer's antiviral treatment for COVID-19.

FILE - This image provided by Pfizer shows the company's COVID-19 Paxlovid pills. Pfizer's and Merck's COVID-19 pills that were supposed to be an important weapon against the pandemic in the U.S. are in short supply and have played little role in the fight against the omicron wave of infections. (Pfizer via AP, File)

The authorization posted to the Health Canada website this morning says the treatment is greenlighted for adult patients with mild or moderate COVID-19 who are also at high risk of becoming more seriously ill.

Health Canada did not authorize it for use on teenagers.

It is also not authorized for use on patients who are already hospitalized because of COVID-19.

Paxlovid is a treatment that uses a combination of drugs to prevent the virus that causes COVID-19 from replicating once it has infected a patient.

Clinical trials show it was almost 90 per cent effective at preventing serious illness in higher-risk patients who received it within the first five days of being infected.