Centene Corp. will buy smaller rival WellCare Health Plans Inc. for $15.27 billion in stock and cash, in a move to bulk up the U.S. health insurer’s government-backed Medicare and Medicaid businesses while reducing exposure to Obamacare healthcare exchanges.

The U.S. government said it would increase by 3.4 percent on average 2019 payments to the health insurers that manage Medicare Advantage insurance plans for seniors and the disabled, a higher-than-expected rise reflecting a projection of higher medical cost growth.