Preliminary tests indicate the Covid-19 antibody drug cocktail from Regeneron Pharmaceuticals Inc. loses effectiveness against Omicron, the company said Tuesday, a sign that some products in an important class of therapies might need modifying if the new strain becomes widespread.

Separate testing of another authorized Covid-19 antibody drug cocktail, from Eli Lilly & Co., indicates it also isn’t as effective against Omicron, outside scientists said. Lilly said it is testing the new variant against its antibody treatment and wouldn’t speculate on what the results will be…

Researchers say some antibody therapies are likely to be especially vulnerable to Omicron because it contains mutations to the spike protein that the Regeneron and Lilly drugs target, while other drugs should hold up well because they attack elements of the virus unchanged in the variant.