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Merck & Co.'s COVID-19 antiviral pill was endorsed by a World Health Organization panel for patients in the early stages of disease who face high risk of hospitalization.

The WHO panel of international experts, which looked at data from six randomized clinical trials involving more than 4,000 patients, found a moderate certainty that Merck's molnupiravir reduces the risk of hospital admission and recovery time. The effect on mortality wasn't so clear. The decision was published Thursday in the BMJ medical journal.

Merck's pill is used in the US and UK to treat COVID patients at high risk of severe illness, but its mechanism of action and lesser efficacy have prompted a shift toward Pfizer Inc.'s Paxlovid and other drugs. US National Institutes of Health guidelines specify that molnupiravir should be used only when other medications for outpatients can't be given.

Molnupiravir shouldn't be used for young and healthy patients, pregnant and breastfeeding women, the experts said. They couldn't make a recommendation for people who were severely ill because of a lack of data, they said.

The group, which has approved medicines such as Eli Lilly & Co.'s rheumatoid arthritis drug baricitinib and GlaxoSmithKline Plc's monoclonal antibody sotrovimab for Covid, said it's reviewing its clearance of Gilead Sciences Inc.'s remdesivir due to new trial data. It's also preparing a recommendation for Paxlovid.

Merck on Feb. 3 trimmed the upper end of its 2022 forecast for molnupiravir sales to $6 billion, down from its earlier prediction that the drug might log up to $7 billion by year end. The US drugmaker has been developing molnupiravir with partner Ridgeback Biotherapeutics LP.

The pill is only about 30% effective at preventing Covid deaths and hospitalizations among high-risk patients, compared with about 90% efficacy for Paxlovid, studies have shown.