The company said on Friday that it found that the pill reduced the risk of hospitalization and death in high-risk Covid patients by 30 percent.
Health officials around the world are counting on the drug molnupiravir to save lives and reduce the burden on hospitals, but the lower efficacy is a disappointment. The Food and Drug Administration is reviewing a similar offering from Pfizer.
A panel of advisers to the F.D.A. will meet on Tuesday to discuss the treatment of high-risk Covid patients.
The reviewers found that the drug was effective in preventing severe disease and that there were no major safety concerns.
The reviewers said they only became aware of the updated efficacy estimate this week. The panel will meet on Tuesday.
The drug reduced hospitalization and death by 50 percent, according to an initial estimate from the company. The figure was revised on Friday from more than 1,400. The participants who received molnupiravir had a 6.8 percent risk of being hospitalized and one patient died. Nine people died after receiving a placebo, and they had a 9.7 percent risk of being hospitalized.
Dr. David Boulware, an infectious disease researcher at the University of Minnesota, said he expected the drug to get emergency authorization. The treatment could be approved in the United States as soon as next week if the expert committee approves it.
The reduction in hospitalization is less, but there is still a big mortality benefit if you start early.
He said that molnupiravir will probably be considered a lower-tier treatment for people who can't get or don't want more effective treatments.
Monoclonal antibody drugs have been found to reduce hospitalizations and deaths by at least 70 percent. Paxlovid, which was found in a clinical trial to cut the risk of hospitalization and death by 89 percent, could be available within weeks. Fluvoxamine appears to be just as effective as molnupiravir.
The first in a new class of antiviral treatments for Covid that are expected to reach many more people than other treatments have been developed by Merck. Public health experts say that the pills have the potential to prevent illness and save lives.
