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A logo at a Pfizer Inc. facility in Puurs, Belgium, on Nov. 10, 2020. MUST CREDIT: Bloomberg photo by Geert Vanden Wijngaert.
A logo at a Pfizer Inc. facility in Puurs, Belgium, on Nov. 10, 2020. MUST CREDIT: Bloomberg photo by Geert Vanden Wijngaert. (Geert Vanden Wijngaert)

New study data showed Pfizer’s experimental Covid-19 pill was highly effective at keeping patients out of the hospital, but less adept at erasing milder symptoms often associated with breakthrough infections.

Pfizer disclosed findings from two studies in a statement Tuesday. In one, its treatment, Paxlovid, failed to meet the primary goal of reducing self-reported symptoms in 673 adults at standard risk of developing Covid-19 complications. The drug showed a trend toward reducing hospitalizations in the group by 70%, however.

In the other study, the treatment remained 89% effective in preventing hospitalizations in high-risk unvaccinated people when used within 3 days of the appearance of symptoms. That confirmed Pfizer’s earlier analysis of results from a smaller number of patients.

The complicated results suggest that the pill remains likely to become a standard treatment for Covid patients at risk of developing severe disease. But the mixed reading in healthier patients shows more study is likely to be needed before it becomes a go-to option for vaccinated individuals who develop frustrating but not life-threatening infections.

The high-risk finding “underscores the treatment candidate’s potential to save the lives of patients around the world,” Pfizer Chief Executive Officer Albert Bourla said in the statement. “If authorized or approved, this potential treatment could be a critical tool to help quell the pandemic.”

The shares rose 0.3% as of 9:44 a.m. in New York. A separate study by South African researchers found that a two-shot course of Pfizer and BioNTech SE’s Covid vaccine prevented 70% of hospitalizations and a third of infections caused by the omicron variant. The findings from Discovery Ltd., South Africa’s largest health insurer, were based on about 78,000 Covid test results.

Pfizer said lab tests indicate that Paxlovid will also retain its activity against omicron, as expected. The medication targets an internal protein, called a protease, that isn’t thought to mutate much between variants. By contrast, vaccines take aim at the so-called spike protein, which is highly mutated in omicron and could change more in future variants.

The data in high-risk unvaccinated people looks clear-cut. If confirmed by regulators, the results could pave the way for an emergency clearance and widespread use in such patients as soon as Pfizer is able to produce it in large quantity.

In an interview, Pfizer senior vice president Annaliesa Anderson said the company started submitting data needed to gain a U.S. emergency authorization in high-risk patients “a while ago,” and that it would provide the new updated data to U.S. regulators shortly.

The other tranche of study data suggests a more complicated path for using the drugs in patients at lower risk of complications from the virus.

The standard-risk trial included vaccinated patients who had at least one risk factor for severe disease and low-risk unvaccinated people. Pfizer didn’t release additional details on the primary endpoint of self-reported symptoms. It said in its statement that an independent data monitoring committee had recommended that the trial continue.

Adverse events were similar between the drug and placebo group in both trials, Pfizer said, suggesting there are no major side effect problems so far.

In the standard-risk trial, the apparent decline in hospitalizations wasn’t statistically significant due to the small numbers of patients involved, said Anderson, who heads Pfizer’s hospital unit, which includes antiviral research.

Anderson said the company had focused on symptom reduction as the primary goal of the standard risk study, not hospitalization, as it had figured proving a reduction in hospitalizations would be hard to achieve in the lower-risk people.

“We are working through what our path forward will be in this patient population,” Anderson said, adding that the company should have full results from the standard-risk trial “soon.”

From a public-health perspective, a drug that can reduce deaths among the unvaccinated and reduce strain on the health-care system is crucial.

But over the long-term, showing the drug can help the vaccinated as well is also important. Over time, unvaccinated adults are becoming an increasingly smaller minority. And if the immune-evading omicron variant takes over from delta, or at least becomes a major player going forward, less serious Covid cases among vaccinated people may become even more common.

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