A mid-stage trial testing Atea Pharmaceuticals' COVID-19 treatment failed to meet the main goal of reducing the amount of SARS-CoV-2 virus in non-hospitalized patients with mild or moderate disease, the company said on Tuesday.

Atea's shares slumped 70.9% to $11.78 in premarket trading.

The company is developing the oral drug, AT-527, in partnership with Roche ROG.S and both the companies are collaborating on multiple studies of the drug for the treatment of COVID-19.

In the mid-stage study, AT-527 did not show a clear reduction in SARS-CoV-2 viral load in the overall population of patients with mild or moderate COVID-19 compared to placebo, but it showed a reduction in viral load in high-risk patients with underlying health conditions.

Many factors including different variants emerging during the study, greater penetration of vaccinations within the enrolled population could have impacted results, it said.

Atea said based on the latest results and the evolving COVID-19 environment, it is modifying an ongoing late-stage study testing the drug in non-hospitalized patients with mild to moderate COVID-19 to include changes to the trial's main goal and patient population.

As a result, the company now expects late-stage trial data in the second half of 2022, instead of the latter half of this year.

(Reporting by Mrinalika Roy in Bengaluru; Editing by Shailesh Kuber) ((mrinalika.roy@thomsonreuters.com))