The Oracle of Omaha just took a $1.6 billion stake in the battered healthcare giant, sending shares soaring 9% after hours.

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.

Buffett owned UnitedHealth shares before selling his stake in 2010, though his Berkshire Hathaway recently acquired shares.

B stake in UnitedHealth Group Incorporated signals a market shift. Click for why I have now upgraded UNH stock to Buy.

Warren Buffett's Berkshire Hathaway built a $1.6 billion stake in UnitedHealth last quarter, marking one of its last wagers with the investor as CEO.

The blue-chip Dow was on track to open at a record high on Friday, underpinned by expectations of an interest rate cut in September and gains in UnitedHealth's shares after Berkshire Hathaway raised its stake in the health insurer.