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Merck’s Covid-19 pill showed activity against omicron in six laboratory studies that raise confidence in the ability of the new therapy to battle the contagious, dominant variant.

The independent studies from the U.S. and five European countries examined the impact of Merck’s molnupiravir and other antivirals against variants of concern including omicron, Merck and partner Ridgeback Biotherapeutics said Friday in a statement.

Merck’s drug was cleared by regulators in the U.S. and U.K. to treat Covid patients at high risk of severe illness after it showed 30% effectiveness in preventing death or hospitalization. Because it works by inducing genetic errors and is less effective than competing drugs, U.S. National Institutes of Health guidelines recommend that it be used only when other outpatient treatments, including Pfizer’s Paxlovid pill, can’t be.

The findings “provide additional confidence in the potential of molnupiravir as an important treatment option for certain adults with mild to moderate Covid-19 who are at high risk for progressing to severe disease,” Dean Li, president of Merck Research Laboratories, said in the statement.

The European Union’s regulator is still reviewing Merck’s drug. Meanwhile, the U.K. said people with weakened immune systems will start getting access to Pfizer’s Paxlovid on Feb. 10, a move that could potentially save thousands of lives and help ease pressure on hospitals.

Paxlovid reduced the risk of hospitalization or death among people at high risk of severe Covid illness by 88% in clinical trials, the government said.

Other treatments recommended for Covid outpatients include sotrovimab, a monoclonal antibody therapy from GlaxoSmithKline and Vir Biotechnology, and Gilead Sciences’ remdesivir.

Merck shares were down 1.1 % at 10:05 a.m. in New York.