Anthem, the nation’s second-largest health insurer, will acquire Cigna, the nation’s fifth largest, for $48.4 billion, the companies announced Friday, creating a health insurance behemoth that raises fresh questions about competition in the industry.

The deal values Cigna’s at $188 per share, a 38 percent premium from its closing price of $154 a share on Thursday. Cigna shareholders will receive a combination of stock and cash in the transaction.

A merged company would serve 53 million people and is part of a dramatic, long-predicted reshaping of the health insurance landscape as a result of the Affordable Care Act. UnitedHealthcare has 45 million members, and Humana and Aetna announced they would merge in July, creating a company serving 33 million people. The new company is projected to generate $115 billion in annual revenues.