Pfizer says antiviral COVID-19 pill cuts risk of severe disease by 89% in high-risk adults

Pfizer Inc. said Friday that its experimental antiviral pill for COVID-19 cut rates of hospitalization and death by nearly 90 per cent in high-risk adults, as the drugmaker joins the race to bring the first easy-to-use medication against the coronavirus to the U.S. market.

Drugmaker says it will ask U.S. FDA to authorize the pill

Pfizer’s antiviral COVID-19 pill shows promise

11 months ago
Duration 1:58
Pfizer released preliminary clinical trial results for its antiviral pill, showing an 89 per cent reduction in risk of hospitalization or death in patients with COVID-19 symptoms.

Pfizer Inc. said Friday that its experimental antiviral pill for COVID-19 cut rates of hospitalization and death by nearly 90 per cent in high-risk adults, as the drugmaker joins the race to bring the first easy-to-use medication against the coronavirus to the U.S. market.

Currently all COVID-19 treatments used in the U.S. require an IV or injection. Competitor Merck's COVID-19 pill is already under review at the Food and Drug Administration (FDA) after showing strong initial results. On Thursday, the United Kingdom became the first country to OK it.

Pfizer said it will ask the FDA and international regulators to authorize its pill as soon as possible, after independent experts recommended halting the company's study based on the strength of its results. Once Pfizer applies, the FDA could make a decision within weeks or months. If authorized, the company would sell the drug under the brand name Paxlovid.

At a briefing on Friday looking at COVID-19 modelling in Canada, Chief Public Health Officer Theresa Tam told reporters that the Pfizer antiviral product and the Merck pill recently authorized for use in the U.K. are under review by Health Canada.

WATCH | Pfizer COVID-19 antiviral pill offers huge hope, says specialist:

Pfizer COVID-19 antiviral pill offers huge hope, says specialist

11 months ago
Duration 4:50
Pfizer's experimental antiviral pill for COVID-19 has great potential to drive down mass hospitalizations and reduce death, says infectious diseases specialist Dr. Zain Chagla. 'There is a lot of optimism,' he said. (Bebeto Matthews/The Associated Press)

However, Health Canada later clarified that it has not received a submission from Pfizer for its antiviral pill and is currently reviewing only the Merck antiviral.

"Health Canada has had ongoing discussions with Pfizer on the development of their new antiviral drug for the treatment of COVID-19. They have just ended their clinical trials, and have not yet filed formal submissions with any regulator," the department said in an emailed statement to CBC News. 

"Should Health Canada receive an application from Pfizer, it will be reviewed on a priority basis."

Researchers worldwide have been racing to find a pill against COVID-19 that can be taken at home to ease symptoms, speed recovery and reduce the crushing burden on hospitals and doctors.

Pfizer released preliminary results Friday of its clinical trials. Patients who received the company's drug along with another antiviral within three days of developing COVID-19 symptoms had an 89 per cent reduction in their combined rate of hospitalization or death after a month, compared to patients taking a placebo pill.

Fewer than one per cent of patients taking the drug needed to be hospitalized and no one died. In the comparison group, seven per cent were hospitalized and there were seven deaths.

"We were hoping that we had something extraordinary, but it's rare that you see great drugs come through with almost 90 per cent efficacy and 100 per cent protection for death," said Dr. Mikael Dolsten, Pfizer's chief scientific officer, in an interview.

Patients who took the antiviral drug within five days of the onset of symptoms had slightly lower (85 per cent) reduction in their combined rate of hospitalization or death, compared to a placebo group. The fact that patients who received the drug earlier had better results underscored the need for speedy testing and treatment. 

Study participants were unvaccinated, with mild-to-moderate COVID-19, and were considered high risk for hospitalization due to health problems like obesity, diabetes or heart disease. Treatment lasted for five days. 

Pfizer reported few details on side-effects but said rates of problems were similar between the groups at about 20 per cent.

An independent group of medical experts monitoring the trial recommended stopping it early, which is standard procedure when interim results show such a clear benefit. The data has not yet been published for outside review, the normal process for vetting new medical research.

Pfizer CEO Albert Bourla, seen in Greece earlier this month, said in a statement that the data suggests 'that our oral antiviral candidate, if approved or authorized by regulatory authorities, has the potential to save patients’ lives, reduce the severity of COVID-19 infections and eliminate up to nine out of ten hospitalizations.' (Giannis Papanikos/The Associated Press)

Top U.S. health officials continue to stress that vaccination will remain the best way to protect against infection. But with tens of millions of adults still unvaccinated — and many more globally — effective, easy-to-use treatments will be critical to curbing future waves of infections.

FDA to review Merck's pill

The FDA has set a public meeting later this month to review Merck's pill, known as molnupiravir. The company reported in September that its drug cut rates of hospitalization and death by 50 per cent. Experts warn against comparing preliminary results because of differences in studies.

Although Merck's pill is further along in the U.S. regulatory process, Pfizer's drug could benefit from a safety profile that is more familiar to regulators with fewer red flags. While pregnant women were excluded from the Merck trial due to a potential risk of birth defects, Pfizer's drug did not have any similar restrictions. The Merck drug works by interfering with the coronavirus's genetic code, a novel approach to disrupting the virus.

Pfizer's drug is part of a decades-old family of antiviral drugs known as protease inhibitors, which revolutionized the treatment of HIV and hepatitis C. The drugs block a key enzyme that viruses need to multiply in the human body.

The drug was first identified during the SARS outbreak originating in Asia in 2003. Last year, company researchers decided to revive the medication and study it for COVID-19, given the similarities between the two coronaviruses.

The U.S. has approved one other antiviral drug for COVID-19, remdesivir, and authorized three antibody therapies that help the immune system fight the virus. But they have to be given by IV or injection at hospitals or clinics, and limited supplies were strained by the last surge of the delta variant.

Shares in New York-based Pfizer Inc. gained 11 per cent to close at $48.61 US on Friday.


  • An earlier version of this story said that Health Canada was reviewing the Pfizer and Merck antiviral COVID-19 pills. Health Canada later clarified that it has not yet received a submission from Pfizer for its antiviral pill.
    Nov 05, 2021 12:10 PM ET

With files from CBC News

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