(Bloomberg) -- CVS Health Corp.’s deal to buy insurer Aetna Inc. for about $67.5 billion could be just the start of a new wave of health-care takeovers.

The merger announced Sunday will leave one less independent player in the complex web of insurers, retailers and other middlemen that sit between patients and their care -- and who are under pressure to reduce costs.

CVS, based in Woonsocket, Rhode Island, made its move on Aetna less than a year after two major health-insurance takeovers were blocked by the Justice Department on antitrust grounds, and as rumors swirl about a disruptive entry into health care by tech retail giant Amazon.com Inc.

“You could see potentially two other big deals,” such as an insurer buying a rival or a pharmacy-benefit company, said Jeff Jonas, a portfolio manager at Gabelli & Co., which owns shares of Aetna and CVS. Smaller players, like walk-in urgent-care clinics, could also get snapped up by health insurers, he said.

Here’s who’s left:

Health Insurers

Insurers are looking for two things: more control over how their consumers get care, and scale. They also have something buyers want: the ability to steer millions of customers to services and health providers.

Among the most likely deals is a merger between Cigna Corp. and Humana Inc., the fourth and fifth largest publicly traded health insurers by market value, says Jonas. Such a combination would test antitrust enforcers after they blocked deals between Aetna and Humana, and Anthem Inc. and Cigna.

WellCare Health Plans Inc. and Centene Corp., freestanding insurers that offer government plans, could become targets, according to Matthew Borsch, an analyst at BMO Capital Markets.

Stranger combinations are possible, as well. Wal-Mart Stores Inc. could buy Humana, Leerink Partners analyst Ana Gupte said Monday. The companies already have a co-branded Medicare drug plan that steers patients to Wal-Mart stores.

Express Scripts

CVS’s biggest competitor in the pharmacy-benefits-management space is Express Scripts Holding Co. The PBM is at a vulnerable point after its largest client, Anthem, recently said it plans to leave.

Express Scripts’ chief executive has said the company isn’t looking for a deal -- but would listen to the pitch. The company’s shares rose as much as 6 percent on Monday -- their best intraday gain in a year.

There’s even an outside chance that Express Scripts could be acquired by Anthem, now that CVS is buying Anthem’s direct rival, said Jonas of Gabelli. Anthem, which has said Express Scripts overcharged it for drugs, plans to drop the PBM when their contract expires at the end of 2019.

Standalone Pharmacies and Clinics

Express Scripts could also combine with a retail pharmacy chain like Walgreens Boots Alliance Inc., Charles Rhyee, an analyst at Cowen & Co., said in October.

The pharmacy chain has suffered from the same retail trends as many other retailers, and Express Scripts would help it diversify. Walgreens CEO Stefano Pessina has talked in the past about the benefits of vertical integration. But in an interview in January, the chief executive said he wasn’t interested in acquiring a PBM.

Walgreens is still busy with its purchase of over 1,900 Rite Aid Corp. stores, a deal that finally cleared regulators in September. While Walgreens will “definitely will be under pressure” to match CVS’s new services, Jonas said, so far the company has favored joint ventures and partnerships over outright acquisitions.

Urgent-care clinics offer a growing business with the potential for higher profit margins than the highly-regulated insurance business, according to the Gabelli portfolio manager.

Regional clinic chains are already getting acquired. UnitedHealth Group Inc.’s Optum unit bought the MedExpress chain of urgent-care centers in 2015, for an undisclosed amount. This year private equity firm Warburg Pincus snapped up CityMD, the leading urgent care provider in the New York City metropolitan area.

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