NEW YORK: Regeneron Pharmaceuticals Inc’s COVID-19 antibody drug could be less effective against Omicron, it said on Tuesday, adding to fears about the efficacy of existing treatments after Moderna’s top boss raised similar concerns about the company’s vaccine.

Global markets tumbled after comments from Moderna’s chief executive officer rekindled worries that the variant may weigh on a nascent global economic recovery.

Based on its study of Omicron’s individual mutations, “there may be reduced neutralization activity of both vaccine-induced and monoclonal antibody conveyed immunity”, Regeneron said, adding that the analysis included its COVID-19 antibody cocktail, REGEN-COV. The company said it was doing further study to quantify the potential impact using the variant’s genetic sequence.

One of the antibodies used in the treatment will likely take a hit, the other less so, CEO Len Schleifer said in a CNBC interview. “Just like vaccines will have to adapt, we’re probably going to have to constantly adapt our monoclonals.”

Eli Lilly and Co, which makes a similar monoclonal antibody treatment, is also working to understand neutralization activity of its therapies on Omicron, the company told Reuters in an e-mailed statement. Regeneron shares fell about 3% in morning trading, while those of Lilly shed 2.5%.

Rival Vir Biotechnology Inc said based on the Omicron sequence its antibody therapy, sotrovimab, will likely maintain potency against the variant. The company is “working to confirm this in the lab as a matter of urgency”, it added.

Gilead Inc said it believed its intravenous therapy, Remdesivir, currently the only antiviral approved for treating COVID-19, will continue to be effective against currently identified variants, including Omicron. The U.S. Food & Drug Administration said on Tuesday it was evaluating the effectiveness of authorized COVID-19 vaccines against Omicron and was expecting to have more information in the next few weeks.