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GlaxoSmithKline headquarters in London on Jan. 17,.HANNAH MCKAY/Reuters

The U.S. health regulator said on Tuesday GlaxoSmithKline and Vir Biotechnology’s antibody therapy was no longer authorized to treat COVID-19 in the U.S. due to an increase in the proportion of cases caused by the Omicron sub-variant.

The agency pulled its authorization for the therapy sotrovimab in much of the U.S. northeast last month. The highly contagious BA.2 coronavirus sub-variant is estimated to cause about three of every four COVID-19 cases in the U.S. now, according to government data.

Vir Biotechnology’s shares fell nearly 10% in afternoon trading.

GlaxoSmithKline and Vir have said treatment with sotrovimab retains neutralizing activity against the BA.2 sub-variant, but others, including researchers from Columbia University, found it did not.

Last month, the companies said they were preparing a package of data in support of a higher dose for sotrovimab than the currently authorized 500 mg for the BA.2 sub-variant.

The U.S. Food and Drug Administration’s move on Tuesday comes as a blow as GlaxoSmithKline and Vir saw high demand for sotrovimab after it became one of the few COVID-19 treatments shown to have worked against the Omicron variant.

The companies did not immediately respond to a Reuters request for comment.

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