Pfizer’s Covid pill remains 89% effective in final analysis, company says

Paxlovid, Pfizer’s pill to treat Covid-19, retained its 89% effectiveness in preventing hospitalizations and death in the comprehensive results of a study of 2,246 high-risk patients, the company said on Tuesday.

In early November, Pfizer had published the interim results of the first 1,219 patients in the study. But another oral antiviral targeting Covid, from Merck and Ridgeback Biotherapeutics, had seen estimates of its effectiveness in preventing hospitalization drop from 50% to 30% between an intermediate outcome and a final outcome. An expert panel advising the Food and Drug Administration on Nov. 30 recommended on 13-11 that the Merck pill, molnupiravir, be cleared for emergency use. The FDA has not announced a decision.

Oral medications are considered important because they might be much easier to administer to infected people than existing medications like monoclonal antibodies, which need to be infused intravenously or injected.


Experts contacted by STAT heaved a sigh of relief that Pfizer’s results had held up, although all stressed the need to take a more in-depth look at the data, which was shared in a press release, not a scientific publication.

“The protection against hospitalization is obviously fantastic,” said Andrew Pekosz, vice president of microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health. “That number was a large number. The fact that it was kept in this final scan really indicates that it is a very important weapon in our arsenal to fight Covid-19, especially as we are seeing more variants that will reduce this. efficiency number. “


Pfizer also reported the results of a second study in adults with Covid at normal risk of developing serious illness, a group that included people who were vaccinated. This study failed to achieve its primary objective of increasing sustained relief from self-reported symptoms in an interim analysis; the study is continuing. But Pfizer said there was also a decrease in hospitalizations in this group, although the numbers are low.

In the high-risk patient study, called EPIC-HR, 5 of 697 patients who received five-day treatment with Paxlovid were hospitalized or died, compared to 44 of 682 who received placebo. There were no deaths in the Paxlovid group and 9 in the placebo group. Adverse events occurred at similar rates between the placebo and Paxlovid groups, and patients taking Paxlovid were less likely to have a serious problem or to stop taking the drug due to a perceived side effect. The patients in the study were considered to be at high risk because they were not vaccinated and had at least one characteristic or underlying medical condition that increased their risk of Covid-19. These could include being over 65, overweight, or have cardiovascular disease.

The low-risk patient study, called EPIC-SR, showed that 2 of 333 patients who received five-day treatment with Paxlovid were hospitalized compared to 8 of 329 who received placebo. The results were similar in a second analysis, Pfizer said, but barely lacked statistical significance. The rates of adverse events were similar between the drug and the placebo.

Eric Topol, director and founder of the Scripps Research Translational Institute, said that despite the failure of this trial in its primary goal of reducing symptoms, he was encouraged by the consistency between the results. “It all fits together,” he said.

Celine Gounder, clinical assistant professor of medicine and infectious diseases at NYU Grossman School of Medicine and Bellevue Hospital, said she was encouraged that the effectiveness was similar whether the treatment was given in the three days after onset of symptoms or within five days.

“It means you have a bigger window to get diagnosed and get someone medication,” Gounder said. “The impact will be determined by the ability of people to access it on time. The fact that you have a week of working days, for me, is really important.

Paxlovid, if authorized, would be given as two tablets of Paxlovid plus one of ritonavir, another antiviral, twice a day for five days. Ritonavir can interact with many other drugs, which could add logistical barriers to its use.

One of the big concerns, Topol said, was the drug supply. Pfizer says it will have 200,000 drug courses available this year and 80 million available next year. But he feared that was not enough given the waves of Covid that could hit the whole world.

Annaliesa Anderson, senior vice president of Pfizer who has been instrumental in the development of the treatment, said the company is working to increase production, just as it has done with the Covid vaccine that she developed with BioNTech, looking for ways to work with partners to speed up production. “We are doing what we can,” she said.

Anderson said Pfizer has “great confidence” that Paxlovid will remain potent against the Omicron variant based on in vitro data showing that the pill inhibits a key protease enzyme in Omicron. However, she noted, antiviral tests for the new variant have yet to be developed.

She also described the development of the antiviral as, in some ways, bittersweet. Anderson said a highlight in its development was when Covid vaccines were found to be effective, and some people have asked if an antiviral is needed. (This was, she said, because vaccines won’t work for everyone and not everyone will have access to them.) A low point has been the failure of other drugs against Covid because she was concerned that no oral medication would work.

“We all spent a lot of time developing this antiviral,” she said, “and we hoped we didn’t need it.”

Information on how the study represented people of different origins and ethnicities was not immediately available. Pregnant or breastfeeding women were excluded from the trials.