Final study results show Pfizer's experimental COVID-19 pill remained as effective as indicated by preliminary data last month, a major relief after promising data for another oral drug from Merck & Co. failed to hold up in fuller testing.
Pfizer's much-anticipated results, disclosed Tuesday, confirmed its pill Paxlovid cut the risk of hospitalization or death from COVID-19 by 89% compared to a placebo when given to high-risk adults within three days of their developing symptoms. The risk reduction was similar, 88%, when measured within five days of symptoms beginning.
The data were disclosed by Pfizer in a press release. Complete results will be submitted for publication in a peer-reviewed medical journal, the drugmaker said.
Pfizer is already in the process of asking the Food and Drug Administration for emergency authorization of Paxlovid, an application it began last month after a preliminary study analysis showed an identical 89% risk reduction in people with mild or moderate COVID-19 who were at high risk of more severe symptoms. The encouraging efficacy led Pfizer, on the recommendation of independent study monitors, to stop enrolling more volunteers into the trial.
Tuesday's results, by comparison, are from an analysis of all 2,246 participants enrolled in the study, nearly twice as many as were included in the November readout.
While welcome news on their own, Pfizer's findings are even more important after final results for Merck's coronavirus pill molnupiravir showed that drug to be far less effective than it initially appeared — only 30% effective at reducing the risk of COVID-19 hospitalization or death, rather than the roughly 50% first shown in October.
FDA staff have raised questions about molnupiravir's safety as well and, at a Nov. 30 meeting, outside agency advisers were torn on whether its benefits outweighed those risks. Ultimately, they voted 13-10 in favor of the drug, but urged the FDA to place limits around its use. The regulator still has not made a decision on authorization.
A decision could be forthcoming on Paxlovid too, now that Pfizer has final results to share with the FDA. According to the company, only five of the 697 patients treated with Paxlovid within three days of symptoms were hospitalized through the 28 days following trial entry, compared to 44 of the 682 in the placebo group. No deaths were reported among those who received Paxlovid, versus nine who were given a placebo.
Results were comparable for those treated within five days of developing symptoms. Eight of the 1,039 study participants treated with Pfizer's drug were hospitalized, versus 66 of the 1,046 in the placebo group. Twelve placebo recipients died, while there were no deaths among those administered Paxlovid.
Importantly, benefits were consistent in adults over 65, a group particularly vulnerable to COVID-19. Only one of 94 study volunteers in that age group and treated with Paxlovid ended up in the hospital, while 16 of the 98 given placebo were hospitalized and six died.
Strengthening Pfizer's findings were data showing Paxlovid also reduced the amount of circulating virus by about 10-fold — an effect Pfizer claimed is the "strongest viral load reduction reported to date" for a COVID-19 pill.
Rates of side effects were similar between Paxlovid and placebo, and those that occurred were mostly mild. Pfizer didn't disclose specifics, but said there were fewer severe adverse events in treated patients than in placebo recipients. Roughly 2% of those who got Paxlovid dropped out of the trial, versus 4.2% of people in the placebo group.
In a separate trial, though, Pfizer found that Paxlovid isn’t as helpful for people who have already been vaccinated or are otherwise at lower risk of developing severe disease — which could lead regulators to narrow its use to more vulnerable groups. Paxlovid missed its main goal of meaningfully curbing symptoms for four straight days, versus placebo, in that study. The drug did, however, reduce hospitalizations from any cause by 70%. The trial is ongoing.
Pfizer has said that its drug has demonstrated potency against several coronavirus variants and that lab tests indicate it should work against omicron, the fast-emerging strain that's been detected in more than 70 countries so far. Additional lab studies are underway.
The U.S. government last month paid $5.3 billion for 10 million courses, while it's preordered more than 3 million treatment courses of molnupiravir. U.K. regulators cleared Merck's pill for use there in November.