Another 12,600 elderly and disabled patients will experience disruptions in their health care, as primary care doctors connected to Beth Israel Lahey Health lose their in-network status because of changes in a Medicare Advantage plan.

Blue Cross Blue Shield of Massachusetts, the state’s largest health insurer, recently informed patients enrolled in its Medicare Advantage PPO plan that they would need to change insurance plans, find new primary care doctors, or pay higher out-of-network costs to continue to see primary care physicians that are a part of Beth Israel Lahey Health Provider Network. The new policy goes into effect Jan. 1.

The change follows a similar development at Mass General Brigham. Nearly 19,000 Medicare Advantage patients covered by Blue Cross Blue Shield or UnitedHealthcare were recently pushed out of the networks of some Mass General Brigham primary care physician groups. That change also goes into effect Jan. 1.

MGB and Beth Israel Lahey are respectively the largest and second largest health systems in state.

Blue Cross and Beth Israel Lahey said in a joint statement that the change was “mutually agreed” upon.

“This decision was made by Blue Cross and Beth Israel Lahey Health Provider Network as the best way to sustainably manage the care of our Medicare members and patients,” the insurer and health system said in the statement.

The contract termination does not affect patients enrolled in Blue Cross Blue Shield’s Medicare Advantage HMO plan. Unlike the PPO plan, in which patients generally do not need a referral to see specialists, HMO plans have care coordinated through a primary care physician, and require referrals to see other providers in the network.

Additionally, patients with the Blue Cross Medicare Advantage PPO plan will still be able to visit Beth Israel Lahey Health and Cambridge Health Alliance hospitals and specialists in network.

The insurer encouraged members to look at other plan options during upcoming open enrollment as a result of the change, and noted that primary care providers with the Beth Israel Lahey Health Provider Network were still accessible to members enrolled in commercial PPO Blue Cross products.

Blue Cross said it didn’t have other planned changes to its contracting networks, but added that it negotiates contracts with a third of its hospitals and providers each fall, and conversations remained ongoing with some.

Medicare Advantage plans are approved by the federal insurer but offered by private insurers as an alternative to standard Medicare plans. The plans often have enhanced benefits such as vision and dental coverage.

It was unclear why so many Medicare Advantage customers were seeing disruptions with their primary care providers, but the shifts come amid a broader primary care crisis in the state.

Patients cannot find doctors, and a high number of primary care providers in the state are aging, according to a report issued in January by the state Health Policy Commission. The number of new primary care doctors coming into the health care system is not keeping up with departures.

While primary care access is a problem nationwide, it has been a particular challenge in Boston. Staffing company AMN Healthcare disclosed in a recent report that patients in Boston waited an average of 69 days to see a new primary care physician, the longest wait among 15 metropolitan areas in the country, from Atlanta to Washington, D.C.

The longest time to get a new family medicine appointment in Boston stretched 182 days — about six months.

Jessica Bartlett can be reached at jessica.bartlett@globe.com. Follow her @ByJessBartlett.