WASHINGTON — Anthem, the nation’s second-largest health insurer by revenue, will acquire Cigna, the nation’s fifth largest, the companies announced Friday, creating a health insurance behemoth that raises fresh questions about competition in the industry.

The $54.2 billion deal will create the largest private health insurer as measured by the number of members. It values Cigna 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 from five big players to three. The new company is projected to generate $115 billion in annual revenues. UnitedHealth Group has more than 45 million members, and Aetna and Humana announced they would merge in July, creating a company serving 33 million people.

While the major trend of consolidation is the same in these big health care deals, analysts said there are key differences between them. Aetna’s deal to buy Humana greatly expanded its presence in the Medicare Advantage marketplace, whereas the Cigna and Anthem merger will have the biggest ripple effects for the commercial insurance market, where both companies are already major players.

“The consolidation of the largest insurers will certainly reduce competition, leaving employers with fewer options for finding a low-priced plan for employees,” Paula Wade, analyst at Decision Resources Group wrote in an email.

The deal is a ripple effect of the Affordable Care Act, which changed how insurance companies make money. Analysts say that because of new caps on the profit that insurers can make on their plans, the companies have been looking to cut administrative costs by increasing their scale. They will be able to cut redundant departments and also may be able to make investments in new technology more efficiently. The larger companies will also have increased clout in negotiating rates with hospitals and doctors groups.

“We believe that this transaction will allow us to enhance our competitive position and be better positioned to apply the insights and access of a broad network and dedicated local presence to the health care challenges of the increasingly diverse markets, membership, and communities we serve,” said Joseph Swedish, president and chief executive officer of Anthem, in a statement. He will remain chief executive of the new firm.

“Going forward our new company will deliver an acceleration of innovative and affordable health and protection benefits solutions that help address our health system’s challenges and provide supplemental insurance protection, and health care security to consumers, their families, and the communities we share with them,” said David Cordani, president and chief executive officer of Cigna.

Anthem is parent to the well-known Blue Cross and Blue Shield plans in 14 states and a Medicaid plan called Amerigroup in 19 states. Cigna, meanwhile, has well-known insurance plans in the United States and globally. The combined firm will serve individuals, employees and governments. It will close in late 2016, pending regulatory approvals.

Federal and state regulators are likely to scrutinize both of the deals closely, although the companies have argued that the mergers will benefit consumers. The effect on competition will likely vary by geographical market, and possible anti-trust concerns could arise in some areas where the combined companies might control too large a share of the market.

Wade cited the example of Connecticut, where Anthem already holds 35 percent of the commercial market share. Adding Cigna brings their market share to just over half.

“Where an employer might have had his choice of Anthem, Cigna, UnitedHealth and Aetna, after these mergers he’s only got three companies from which to choose,” Wade said.

Some analysts say that the growth of insurance premiums will slow because the industry is regulated and the new companies will be more efficient. For example, Anthem and Cigna are expected to save $2 billion a year from the much larger company within two years, Swedish said Friday morning. Whether those savings trickle down to consumers remains to be seen.