UnitedHealth shares clocked the largest one-day percent increase since March 2020, as tracked by Dow Jones Market Data Group. It was on pace for the best day in 17 years before giving back some of those gains. For the week, shares rose over 21%, the best week since May 2009. Still, the stock is down more than 50% over the past 12 months.

Warren Buffett's Berkshire Hathaway revealed a new stake in troubled insurer UnitedHealth, according to a regulatory filing. The Omaha-based conglomerate bought more than 5 million shares in the health care firm for a stake worth about $1.