Pfizer announced Tuesday that its experimental COVID-19 pill appears effective against the omicron variant.

In an analysis of 2,246 adult participants, the vaccine-maker said results had been consistent with interim analysis announced in November that showed COVID-19 oral antiviral candidate Paxlovid had “significantly reduced the risk of hospitalization or death for any cause by 89% compared to placebo in non-hospitalized, high-risk adult patients with COVID-19 treated within three days of symptom onset.” 

“In a secondary endpoint, PAXLOVID reduced the risk of hospitalization or death for any cause by 88% compared to placebo in patients treated within five days of symptom onset, an increase from the 85% observed in the interim analysis,” Pfizer said in a press release. 


The data has been shared with the Food and Drug Administration (FDA) as part of an ongoing rolling submission for emergency use authorization (EUA). 

Separate laboratory testing shows the drug retains its potency against the omicron variant, the company said, as many experts had predicted. Pfizer tested the antiviral drug against a synthetic version of a key protein that omicron uses to reproduce itself.

“Recent in vitro data confirm that nirmatrelvir is a potent inhibitor of the Omicron 3CL protease, which, combined with existing in vitro antiviral and protease inhibition data from other variants of concern including delta, indicates that PAXLOVID will retain robust antiviral activity against current [variants of concern] as well as other coronaviruses,” Pfizer wrote. 

Paxlovid is comprised of nirmatrelvir and ritonavir tablets.

“This news provides further corroboration that our oral antiviral candidate, if authorized or approved, could have a meaningful impact on the lives of many, as the data further support the efficacy of PAXLOVID in reducing hospitalization and death and show a substantial decrease in viral load,” Pfizer CEO Albert Bourla said in a statement. “Emerging variants of concern, like omicron, have exacerbated the need for accessible treatment options for those who contract the virus, and we are confident that, if authorized or approved, this potential treatment could be a critical tool to help quell the pandemic.”

The updates come as COVID-19 cases, deaths and hospitalization are all rising again and the U.S. hovers around 800,000 pandemic deaths. The latest surge, driven by the delta variant, is accelerating due to colder weather and more indoor gatherings, even as health officials brace for the impact of the emerging omicron mutant.


The FDA is expected to soon rule on whether to authorize Pfizer’s pill and a competing pill from Merck, which was submitted to regulators several weeks earlier. If granted, the pills would be the first COVID-19 treatments that Americans could pick up at a pharmacy and take at home.

Pfizer’s data could help reassure regulators of its drug’s benefit after Merck disclosed smaller-than-expected benefits for its drug in final testing. Late last month, Merck said that its pill reduced hospitalizations and deaths by 30% in high-risk adults.

Both companies initially studied their drugs in unvaccinated adults who face the gravest risks from COVID-19, due to older age or health problems, such as asthma or obesity.

Pfizer is also studying its pill in lower-risk adults — including a subset who are vaccinated — but reported mixed data for that group on Tuesday.

In interim results, Pfizer said its drug failed to meet its main study goal: sustained relief from COVID-19 for four days during or after treatment, as reported by patients. But the drug did achieve a second goal by reducing hospitalizations by about 70% among that group, which included otherwise healthy unvaccinated adults and vaccinated adults with one or more health issues. Less than 1% of patients who got the drug were hospitalized, compared with 2.4% of patients who got a dummy pill.

An independent board of medical experts reviewed the data and recommended Pfizer continue the study to get the full results before proceeding further with regulators.


Across both of Pfizer’s studies, adults taking the company’s drug had a 10-fold decrease in virus levels compared with those on placebo.

The U.S. government has agreed to purchase enough of Pfizer’s drug to treat 10 million people and enough of Merck’s to treat 3 million, pending FDA authorization.

The Associated Press contributed to this report.


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