Paxlovid—Pfizer’s antiviral Covid-19 treatment—is 37% effective at preventing hospitalization or death in high-risk patients compared with no treatment, according to a study published Thursday in the JAMA Network Open, well below the 88% effectiveness rate Pfizer and regulators reported in clinical trials in 2021—though it remains very effective at staving off death.
The study found that when excluding hospitalizations and looking at death alone, the drug is 84% effective.
The observational study analyzed electronic health records from thousands of patients at the Cleveland Clinic Health System in 2022 and early 2023 to determine Paxlovid’s effectiveness, using real-world data rather than the clinical trials that were used before.
The study also found another antiviral Covid-19 treatment, Merck’s Lagevrio, was 42% effective in preventing hospitalization or death and 77% effective against death alone.
WHAT WE DON’T KNOW
Why the effectiveness has fallen. The study authors noted the clinical trials were conducted among unvaccinated patients who had limited natural immunity, whereas this study was conducted in a real-world population including vaccinated and previously infected patients who had some other defenses against the coronavirus. They also noted the original clinical studies were completed when the Delta variant was the most common strain of the virus while their study was conducted when the Omicron variant was, suggesting that the drug could work differently with different strains.
While they note the effectiveness has fallen, the study’s authors still say these drugs are useful tools in fighting Covid-19, arguing both drugs can be used in nonhospitalized Covid-19 patients to prevent the most severe outcomes.
Paxlovid is still “definitely recommended for high-risk patients,” said University of North Carolina professor Danyu Lin, one of the study’s authors, according to Bloomberg.
Paxlovid, a course of oral pills, first became available in December 2021 and is to be taken early in a patient’s infection. They’re designed to prevent patients who already have Covid-19 from becoming hospitalized or dying, particularly patients who are at an elevated risk of severe Covid-19 due to age or medical conditions. New information on Paxlovid’s effectiveness comes amid fears of a new wave of Covid-19 this fall. In the week ending September 9, 20,538 people were hospitalized for Covid-19, a 7.7% increase over the week prior, according to the Centers for Disease Control and Prevention. Since the onset of the pandemic, 1.14 million people have died of the virus.
Nirmatrelvir or Molnupiravir Use and Severe Outcomes From Omicron Infections (JAMA Network Open)