The new year brought significant changes in market share to the Medicare Advantage mix in the Philadelphia region.

In South Jersey, AmeriHealth New Jersey's decision to stop selling Medicare Advantage plans, which is a private form of the federal health insurance for seniors, opened the door for Aetna to surge to 62 percent of the market in Burlington, Camden, and Gloucester Counties this month from 46 percent a year ago, according to data from the Centers for Medicare and Medicaid Services.

Horizon Blue Cross Blue Shield of New Jersey more than doubled its share, to 20.5 percent from 9.4 percent. The third-biggest provider in the three counties is UnitedHealthcare, with a share of 14.7 percent.

AmeriHealth New Jersey, which is owned by Philadelphia's Independence Health Group, had 36 percent of the market last year. The company said in October that it was dropping its Medicare Advantage plans for reasons including "increased utilization and inadequate funding."

In doing so, AmeriHealth missed out on an overall surge in Medicare Advantage enrollment in the three counties to 46,498 this month from 38,708 last January.

A federal judge on Monday blocked Aetna's planned acquisition of Humana Inc. because the combination would eliminate competition in 364 counties. The only Philadelphia-area county on the list was Chester, where the combined operations of Aetna and Humana would have had 45 percent of the market, based on this month's enrollment data. That would match Independence Blue Cross's share in Philadelphia.

Federal sanctions barring Cigna from marketing last fall and enrolling new customers in its Bravo Health plans were the biggest factor causing market-share shifts in the five-county Southeastern Pennsylvania area. Cigna's share fell to 18.3 percent from 22.3 percent.

The federal government imposed the penalty last January because of "widespread and systemic failures impacting Cigna enrollees' ability to access medical services and prescription medications," the sanctions letter said.

Cigna said it remains committed to seniors in the Philadelphia area. "We have made significant progress addressing the sanctions and are investing in our capabilities," a Cigna spokeswoman said.

The biggest market share gain in Southeastern Pennsylvania went to UnitedHealthcare, which added 7,810 members and expanded its share to 7.8 percent from 4.5 percent a year ago.

Independence and Health Partners Plans also picked up significant share.

Not having a big impact on the Medicare Advantage market this year was the entry of western Pennsylvania health-care giant UPMC, which picked up just 55 members in Philadelphia.

The small start was not unexpected.

"As we have seen in our 21 years of experience, it's important to gain trust and confidence in our brand, offer affordable  products with an excellent network, and provide award-winning customer service," UPMC said. "We understand it will take time to build that presence in the Philadelphia market."