A Covid-19 antibody treatment developed by GlaxoSmithKline PLC and Vir Biotechnology Inc. was effective against the Omicron variant in early laboratory studies, the companies said, setting it apart from similar therapies that appear to work less well against the highly mutated strain.

The companies said Thursday that they had tested the drug, called sotrovimab, against certain individual mutations found in Omicron, which has now been detected in at least 24 countries, including the U.S. Glaxo and Vir said the findings were preliminary and they would need to test the treatment against the whole of the mutated spike protein found in the variant to confirm the result. The companies published a preliminary research paper on the findings, which haven’t yet been peer reviewed.