In New York, hospital administrators at NewYork-Presbyterian, N.Y.U. Langone and Mount Sinai all said in recent days that they would stop giving patients the two most commonly used antibody treatments, made by Eli Lilly and Regeneron, according to memos obtained by The Times and officials at the health systems.

“This is a dramatic change just in the last week or so,” said Dr. Daniel Griffin, an infectious disease specialist at Columbia University in New York. “And I think it makes sense.”

Federal health officials plan to assess at the end of this week whether to pause shipments of the Eli Lilly and Regeneron products to individual states, based on how dominant Omicron becomes in different regions of the country, according to a senior administration official who spoke on condition of anonymity.

The one monoclonal antibody treatment that has performed well against Omicron in laboratory experiments is also the most recently authorized: sotrovimab, made by GlaxoSmithKline and Vir Biotechnology and cleared in May.