Pfizer COVID-19 Antiviral Pill Cuts Hospitalization and Death by 89%

Pfizer headquarters.

Pierre Suu / Contributor / Getty Images

Key Takeaways

  • According to Pfizer, their COVID-19 antiviral pill called Paxlovid significantly reduces the risk of hospitalization and death.
  • Paxlovid is a protease inhibitor drug, which is different from Merck’s antiviral pill.
  • Pfizer’s clinical trials were stopped early because of the overwhelming efficacy of the drug.

Last week, Pfizer reported that their oral antiviral pill for COVID-19, Paxlovid, significantly reduced the risk of severe outcomes for people with COVID-19.

COVID-19 patients who received the pill three days after their symptoms began had an 89% reduced risk of hospitalization and death compared to those who received a placebo. The researchers also observed similar results for people who were treated within five days of the development of their symptoms.

Since intital news reports of the antiviral in May, Pfizer plans to submit their data to the Food and Drug Administration (FDA) to apply for an Emergency Use Authorization (EUA) as soon as possible.

The COVID-19 antiviral pill developed by Merck & Co. and Ridgeback Biotherapeutics LP, molnupiravir, is already under review by the FDA. A decision could arrive within weeks. If these antiviral drugs are authorized for use by the FDA, they will be the first available COVID-19 oral medications in the U.S.

How Is Pfizer’s Pill Different From Merck’s?

Antiviral medicines inhibit the replication of viruses in different ways, making it more difficult for the virus to reproduce.

Merck and Pfizer’s pills are both oral antivirals, but they target the process of replication differently, Geoffrey Chupp, MD, Yale Medicine pulmonologist and professor of medicine at Yale School of Medicine, told Verywell.

Molnupiravir works by significantly increasing the number of mutations as the virus tries to replicate, preventing it from effectively reproducing.

“In contrast, Pfizer’s antiviral Paxlovid inhibits crucial enzymes, known as proteases, which break viral proteins down so they can reassemble into other proteins needed to replicate,” Vincent Hsu, MD, executive director of infection control at AdventHealth, told Verywell. 

Paxlovid is a protease inhibitor antiviral therapy for COVID-19 that combines PF-07321332—an antiviral drug developed by Pfizer to block an enzyme that the SARS-CoV-2 needs to replicate—and ritonavir, an existing antiretroviral medication. Ritonavir helps slow down the metabolism of PF-07321332 so it maintains a higher concentration in the body to fight the virus.

The combination drug Paxlovid is intended to be prescribed early on in the course of the COVID-19 disease to avoid severe illness or outcomes.

“Protease inhibitors as a class of drugs are not new,” Hsu said. “Effective protease inhibitors are already available against HIV and hepatitis C, but each type of virus has unique proteases, so this is a new antiviral product within an existing class of drugs.”

What This Means For You

Currently, there are no COVID-19 antiviral pills approved for use in the U.S. But they could be available soon.

Why Did Pfizer Stop Clinical Trials Early?

In consultation with the FDA, an independent data monitoring committee recommended that Pfizer stop their clinical trial enrollment early.

“Trials are designed with pre-specified interim analyses to determine efficacy and safety,” Chupp said. “If the interim results meet these data points, the Data and Safety Monitoring Board (DSMB) may decide to stop the study due to futility, safety, or strong efficacy, as is the case with the Pfizer protease inhibitor.”

As with most other clinical drug trials, approximately half of the enrolled patients randomly received the Pfizer drug while the other half receive a placebo, then the outcomes were compared between the two groups, Hsu said.

For instance, among the patients who were treated within three days of symptom onset, only 0.8% of people who received the Paxlovid medication were hospitalized, while 7.0% of those who received the placebo were either hospitalized or died.

“Because the results overwhelmingly showed the drug reduced hospitalizations and deaths, it is a standard practice because of ethical considerations to stop the trial early,” Hsu said. “Continuing to enroll patients to receive the placebo, i.e., withholding the Pfizer antiviral study drug, would be inappropriate when the investigators are aware of the significant impact that the drug has in reducing hospitalizations and deaths.”

Experts say the FDA will likely come to a decision sooner than previously expected.

"Given that no additional data will be collected, it is anticipated that Pfizer will submit its data to the FDA earlier than expected, which would result in an earlier timeline for FDA emergency authorization," Hsu added.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Pfizer. Pfizer’s Novel COVID-19 Oral Antiviral Treatment Candidate Reduced Risk Of Hospitalization Or Death By 89% In Interim Analysis Of Phase 2/3 EPIC-HR Study.

  2. Kausar S, Said Khan F, Ishaq Mujeeb Ur Rehman M, et al. A review: Mechanism of action of antiviral drugs. International Journal of Immunopathology Pharmacol.ogy. 2021;35:205873842110026. doi. 10.1177/20587384211002621.

By Carla Delgado
Carla M. Delgado is a health and culture writer based in the Philippines.