Regeneron said its antibody treatment might not be as effective against Omicron, but testing is underway.

Regeneron said on Tuesday that its Covid-19 antibody treatment might be less effective against the Omicron variant of the coronavirus, an indication that the popular and widely beneficial monoclonal antibody drugs may need to be updated in case the new variant spreads aggressively.

The company said that previous laboratory analyses and computer modeling of certain mutations in the Omicron variant suggest that they may weaken the effect of the treatment. But studies using the variant’s full sequences have not been completed, it said.

The company said it had already been testing future antibody drug candidates, and that preliminary analyses indicated that some of those “may have the potential to retain activity against the Omicron variant.” More data is expected in the coming month, it said.

“What we have to admit is, in the course of the past six days, our urgency has increased,” Dr. George Yancopoulos, Regeneron’s president and chief scientific officer, told The Wall Street Journal in an interview. “What started out as a backup plan has now been made a lot more urgent.”

The Omicron variant has caused alarm among scientists because it contains mutations in the spike protein, the target of the government-supplied monoclonal antibody treatments made by Regeneron and Eli Lilly.

Scientists have also been scrambling to gather data on how effective the current vaccines will be against Omicron. Antiviral pills, including drugs from Merck and Pfizer that federal regulators are considering authorizing soon, are expected to hold up well against the variant because they target a different site of the virus from where Omicron’s mutations are clustered.

Monoclonal antibody treatments, given in a single infusion, use lab-made copies of the antibodies that people generate naturally when fighting an infection. They have been shown to significantly shorten patients’ symptoms. Regeneron’s cocktail reduces the risk of hospitalization by 70 percent.

The company said the treatment was effective against the Delta variant, which remains the dominant form of the virus in the United States.