Many of the experts who were opposed to boosters now believe that the shots may offer the best defense against the new variant. The extra doses may slow the spread, at least, buying time for vaccine makers to develop an Omicron-specific formulation, if needed.

“Based on what we know about the potential for immune evasion, I would err on the side of giving the booster,” said Dr. Celine Gounder, an infectious disease specialist at Bellevue Hospital Center who had opposed the Biden administration’s boosters-for-all push…

“If it is highly resistant to antibodies, which seems likely but unproven, then additional doses are appropriate,” said John Moore, a virologist at Weill Cornell Medicine in New York…

“It’s impacting things like elective procedures at multiple hospitals in Massachusetts and elsewhere,” said Dr. Camille Kotton, an infectious disease physician at Massachusetts General Hospital and an adviser to the C.D.C. “We really need to put an end to this.”