How effective is the COVID-19 antiviral Paxlovid?

Two large studies in Canada and the U.K. examined whether the antiviral medication nirmatrelvir-ritonavir, known as Paxlovid, is effective for people at increased risk of severe COVID-19.

The results of two large clinical trials provide new evidence for policymakers, physicians, pharmacists and patients to consider when funding, prescribing or taking Paxlovid.

The study was led by the Upstream Lab at St. Michael’s Hospital in Toronto and the University of Oxford. It was co-authored by Dr. Amanda Condon, head of family medicine in the University of Manitoba’s Max Rady College of Medicine. The Manitoba research was conducted in partnership with UM’s department of family medicine office of research and quality improvement and the College of Pharmacy.

The study was published in the April 23 issue of the New England Journal of Medicine.

The CanTreatCOVID study in Canada and the PANORAMIC study in the UK involved a total of more than 4,200 people and found that Paxlovid does not reduce hospital admissions or deaths in vaccinated adults at higher risk of severe COVID-19, but it does help people recover a few days faster.

“In terms of the use of Paxlovid, guidelines across Canada have evolved from its initial approval through the CanTreatCOVID study to today. They have progressively narrowed and I think that this evidence will further refine them,” said Dr. Andrew Pinto, director of Upstream Lab, who led the Canadian trial.

In Manitoba, guidelines suggest Paxlovid can be prescribed to treat mild to moderate COVID-19 in patients who are experiencing concerning symptoms and are at higher risk of becoming seriously ill or being hospitalized, including those with weakened immune systems.

“Our Manitoba guidelines on who might benefit from Paxlovid are broad,” said Condon. “Our study provides evidence of its effectiveness that can help refine when and whether it is prescribed to ensure optimal outcomes. The results of this trial can inform future prescribing recommendations.”

In January 2022, Health Canada authorized Paxlovid after initial study results revealed a reduced risk of hospitalization and death by nearly 90 per cent in unvaccinated high-risk patients. In contrast, the PANORAMIC trial (December 2021 - March 2024) and the CanTreatCOVID trial (January 2023 - September 2024) studied vaccinated patients.  

“In today’s highly vaccinated populations, the benefits of Paxlovid have fundamentally changed,” said Oxford University’s Dr. Christopher Butler, who led the UK trial. “While people feel better sooner, we found no reduction in the already low rate of hospitalizations or deaths. This provides essential high-quality evidence for optimal, cost-effective targeting of this treatment.”

Paxlovid speeds recovery time in vaccinated patients

Both trials recruited vaccinated adults aged 50 and over, or younger adults with certain health conditions such as diabetes, heart disease or a weakened immune system. All participants tested positive for COVID-19 and had symptoms for five days or less. Almost everyone (about 98 per cent) had already received at least one dose of a COVID-19 vaccine.

Interestingly, the studies revealed that Paxlovid did not reduce the chance of hospitalization or death from COVID-19 in those who were already vaccinated, but patients reported feeling better sooner and were more likely to stay recovered. In PANORAMIC, median recovery time was 14 days with Paxlovid compared to 21 days with usual care. CanTreatCOVID found recovery at six days versus nine days.

CanTreatCOVID was funded by the Canadian Institutes of Health Research (CIHR) and Health Canada, and supported by the Public Health Agency of Canada. CanTreatCOVID involved researchers from across Canada, including University of Manitoba, University of Toronto, McGill University, University of British Columbia, Simon Fraser University, University of Calgary and Memorial University of Newfoundland.  

By Rady Communications Staff