Additional data from Pfizer's clinical trial of its oral Covid-19 antiviral drug confirm the treatment's high level of effectiveness, the company said in a news release Tuesday.
In the final analysis of its Phase 2/3 clinical trial, the antiviral, called Paxlovid, was found to be 89 percent effective at preventing high-risk people from being hospitalized or dying from Covid, the company said.
The findings are consistent with the results of the interim analysis the company released last month, although the full data have not been made public for scientists to review. Pfizer halted its clinical trial based on the interim results and submitted an application to the Food and Drug Administration for emergency use authorization several weeks later.
The FDA has not scheduled a meeting of its advisory committee to review the application.
Experts say an antiviral pill for Covid would have a major impact on the pandemic by making treatment available at home. Current treatments are available only by injection or IV.
“For many, many people this will be a really important drug,” said Ronald Swanstrom, a biochemistry professor at the University of North Carolina School of Medicine.
If authorized, the question becomes availability, said Dr. David Boulware, an infectious disease physician at the University of Minnesota Medical School. How quickly will Pfizer be able to ramp up production of the drug so that people can fill prescriptions?
“Should the U.S. government do something with production to help?” he said. “Is this something where Pfizer needs to partner with others to scale up manufacturing?”
The Biden administration said last month it plans to purchase 10 million courses of Paxlovid, up from its initial plan to purchase 5 million courses.
A full course of Pfizer's treatment is three pills taken twice daily for five days. Two of the pills are an experimental antiviral called nirmatrelvir; the third pill is an existing HIV drug called ritonavir.
The treatment works by preventing the coronavirus from making copies of itself in the body. Paxlovid was shown to work best when it was given within three days of the onset of symptoms, the company said.
Side effects, which were similar in people who received Paxlovid or the placebo, were mostly mild, the news release said. The company did not detail them.
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Pfizer also released interim findings from a second clinical trial that looked at the treatment's effectiveness in low-risk unvaccinated people, as well as in vaccinated people with one or more risk factors for severe illness. According to the findings, Paxlovid did not alleviate Covid symptoms compared to the placebo, but it cut hospitalizations by 70 percent.
Pfizer said lab studies suggest that the treatment is effective against the new omicron variant of the virus, although more research is needed for confirmation.
The FDA's advisory committee voted narrowly last month to recommend an antiviral from the drugmaker Merck for emergency use authorization. The FDA has yet to authorize the drug, called molnupiravir.
Merck's treatment was found to be 30 percent effective at preventing hospitalization or death from Covid in high-risk patients. Advisory committee members expressed concerns about the safety of the drug, including potential risks to pregnant women and their fetuses.
"The difference in efficacy is really striking" between Pfizer and Merck's drugs, said Swanstrom.
Though they are both antivirals, the two treatments work in completely different ways, he said, and the risk to pregnant women should be lower with Pfizer's drug than Merck's.
If Merck's treatment is authorized, it's possible that the FDA could go on to withdraw the authorization, or request more data from Merck, once the Pfizer pill is available, Boulware said.