Early tests suggest that the COVID-19 antibody treatment developed by Regeneron Pharmaceuticals Inc. /zigman2/quotes/203149337/composite REGN +0.34% loses effectiveness against the omicron variant of the coronavirus that causes COVID, but the full impact will only be known in the coming weeks after further testing, the company's president and chief scientific officer George Yancopoulos told the Wall Street Journal on Tuesday. Evercore analysts had raised that issue in a note to clients on Friday. Omicron is the variant from South Africa that was classified a 'variant of concern' by the World Health Organization on Friday, that has led several countries to impose restrictions on travel from there and neighboring countries. Separate testing of the antibody developed by Eli Lilly & Co. /zigman2/quotes/200106384/composite LLY -0.67% suggests it too is less effective against omicron. Researchers say that some antibody therapies are likely to be 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. Yancopoulos said the company is already working on alternative antibodies that should hold up well against the variant. "What we have to admit is, in the course of the past six days, our urgency has increased," Dr. Yancopoulos said in an interview. "What started out as a backup plan has now been made a lot more urgent." Regeneron shares were down 2.7% premarket, but have gained 35% in the year to date, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.15% has gained 24%.