U.S. stock futures fell and investors sheltered in government bonds after drugmakers raised concerns that Covid-19 vaccines won’t work as well against the new Omicron strain.

Futures tied to the S&P 500 fell 0.8%, while blue-chip Dow Jones Industrial Average Futures shed 1%. Futures for the tech-heavy Nasdaq-100 weakened by 0.4%. Major indexes closed higher Monday, rebounding from a sharp selloff last week, as concerns about the variant seemed to ease.