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Atea Pharmaceuticals said Tuesday that its antiviral pill for Covid-19 failed to combat the virus in a mid-stage trial, leading the company to delay its pivotal study by a year.

The disappointing news follows a far more hopeful October update from Merck, whose similar antiviral reduced the chances that patients newly diagnosed with Covid-19 would be hospitalized by about 50% in a Phase 3 study.


There is a desperate need for treatments for early Covid that can be taken as pills. Current treatments, such as remdesivir and monoclonal antibodies, are generally given intravenously or as injections, and are difficult to distribute to large numbers of people. The hope is that pills to treat Covid could be given widely in order to prevent infected people from progressing to severe disease, hospitalization, or death.

Atea, partnered with global drug maker Roche, said its drug, AT-527, failed to beat placebo at reducing the amount of measurable virus in patients with mild or moderate Covid-19, missing the primary endpoint of a 100-patient trial.

As a result, Atea and Roche are rethinking their Phase 3 trial. That study, designed to enroll up to 1,400 patients, has a primary endpoint of reducing the time it takes patients to recover from Covid-19 and secondary goals including preventing hospitalization. In light of the Phase 2 results, Atea and Roche are now considering whether to change the primary endpoint and target population. Data from that study, once expected this year, are now slated for the second half of 2022, Atea said.


AT-527 works similarly to Merck’s drug, molnupiravir, and was widely expected to succeed in clinical development. The problem might have been trial design. While Merck deliberately excluded patients who had been vaccinated for Covid-19, Atea did not, which might have skewed the results, according to the company. Merck also recruited only patients who had at least one risk factor for severe Covid-19, such as obesity or heart disease, while Atea required only a positive test and mild symptoms.

In a subgroup of patients at high risk for severe Covid-19, AT-527 outperformed placebo at reducing virus levels over seven days, Atea said, which could inform the company’s changes to its Phase 3 trial.

“Based on what we know now, this actually is not surprising, as other direct-acting antivirals, including molnupiravir, have shown similar outcomes in the mild-to-moderate outpatient population,” Atea CEO Jean-Pierre Sommadossi said on a conference call with analysts Tuesday. “What is reassuring is that viral reduction … was observed in high-risk patients with underlying health conditions.”

The news is a bitter disappointment for Atea, which has spent the past 18 months touting the potential of AT-527, developed as a treatment for hepatitis C, to change the course of the Covid-19 pandemic. The company, which commanded a market value of about $3.4 billion as of Monday, fell 70% in premarket trading on Tuesday.

Merck, partnered with Ridgeback Biotherapeutics, is seeking an emergency use authorization for its Covid-19 antiviral and will make its case to a panel of Food and Drug Administration advisers on Nov. 30. Results for another potential oral Covid-19 treatment, from Pfizer, are expected by the end of the year.

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