The U.S. government has paused the distribution of COVID-19 antibody treatments from Regeneron Pharmaceuticals (REGN.O) and Eli Lilly (LLY.N), saying the therapies were unlikely to be effective against the Omicron coronavirus variant.

The variant has become the dominant strain in the United States with lightning speed, resurrecting restrictions and stretching the country’s testing infrastructure.

The halt on the allocation of the therapies will continue until new data emerges on their efficacy, the U.S. Food and Drug Administration and the office of Assistant Secretary for Preparedness and Response said in a joint statement on Thursday.

German researchers have also found that Eli Lilly and Regeneron’s treatments lose most of their effectiveness when exposed to Omicron in laboratory tests.

The U.S. agencies, however, said GlaxoSmithKline and Vir Biotechnology’s rival drug sotrovimab appeared to work against Omicron.

Sotrovimab shipments, which were paused last month pending efficacy data against the variant, have resumed and delivery of 55,000 doses of the drug has begun, the agencies said.