Merck & Co Inc and partner Ridgeback Biotherapeutics said on Friday six lab studies showed their experimental oral COVID-19 drug molnupiravir was active against the fast-spreading Omicron variant.

The data evaluated the antiviral activity of molnupiravir and other COVID-19 antiviral agents against COVID-19 variants of concern. Molnupiravir is yet to be studied against Omicron in human studies, the companies said.

Molnupiravir and a rival oral pill from Pfizer Inc were authorized in the United States in December and are considered as important tools against Omicron.

Merck expects COVID-19 pill molnupiravir to be effective against Omicron

Pfizer said in December lab data suggested its drug Paxlovid retained its effectiveness against Omicron.

Merck said earlier this month its pill has a mechanism that can work against Omicron and any other variant.

Molnupiravir has been authorized for use in more than 10 countries, including the United States, United Kingdom and Japan.