OTTAWA—Health Canada has approved Pfizer’s antiviral treatment for COVID-19. 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 percent effective at preventing serious illness in higher-risk patients who received it within the first five days of being infected. More Coming.