UnitedHealth rises after Berkshire Hathaway buys new stake

** Shares of health insurer UnitedHealth UNH.N rise 12.8% to $306.16 premarket

** Late on Thursday, Warren Buffett's Berkshire Hathaway BRKa.N acquired 5 million shares, or 0.55% stake, in UNH, according to a regulatory filing

** Berkshire owned 5.04 million UnitedHealth shares worth about $1.57 billion, as of June 30

** Shares of other insurers also rise between 2% and 5% premarket

** Elevance Health ELV.N up 5.1%, Molina Healthcare MOH.N up 4.4% and Centene CNC.N up 4.5%

** Cigna CI.N and Humana HUM.N also up in low trading volumes

** As of last close, UNH down 46.3% YTD, ELV down 19.9%, MOH down 45.2%, CNC down 55.6%, while CI up 5.2% and HUM up 10.9%