Major health insurance stocks largely lagged behind a broader market advance Wednesday after Congress reached a last-minute deal to keep the U.S. economy from hitting a so-called "fiscal cliff" of tax hikes and deep spending cuts.

A bill that cleared Congress late Tuesday averted the tax hikes and delayed the spending cuts for a couple months. Analysts saw the agreement as a mixed bag for health insurers.

Bernstein Research analyst Ana Gupte called it a "modest positive" for the sector. Gupte said in a research note the delay in spending cuts means insurers won't have to deal with a planned, across-the-board spending cut for Medicare at least through February. The agreement also averts a steep payment cut for doctors.

Medicare is the federally funded program that provides health coverage for the elderly and disabled people. Analysts see Medicare Advantage plans -- which are privately run versions of the government program -- as a big growth opportunity for managed care.

Economists had worried that a failure to reach a deal that avoids the tax hikes would plunge the U.S. economy into recession.

That threat has been mitigated a bit in the short term, said Morningstar (NASDAQ:MORN) analyst Matt Coffina. He noted that that may help stabilize the number of people with employer-sponsored health insurance, since companies won't have to cut jobs to reduce costs.

But Coffina also said the deal means the uncertainty of the cuts is still playing out. Medicare Advantage plans remain vulnerable to more cuts because they receive a higher level of reimbursement than government-run Medicare.

Analysts and investors who try to predict what companies will do in future quarters dislike uncertainty.

"If they had come up with a grand bargain, we could at least know what it is and then move on," Coffina said.

The Standard & Poor's 500 index climbed 1.7 percent in Wednesday afternoon trading, and only one major health insurer topped that advance. Shares of Cigna (NYSE:CI), which announced that it added some Medicare Advantage membership, rose 2.9 percent, or $1.55, to $55.01.

Shares of UnitedHealth Group (NYSE:UNH), the nation's largest health insurer, was steady at $54.24. Humana (NYSE:HUM) fell less than 1 percent to $68.31. WellPoint (NYSE:ANTM) and Aetna (NYSE:AET) fell less than 1 percent to $60.60 and $46, respectively.

The Motley Fool has no positions in the stocks mentioned above. Motley Fool newsletter services recommend Morningstar, UnitedHealth Group, and WellPoint. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.