Next week, MassHealth will undergo a massive reorganization in which more than 800,000 MassHealth members will be moved to new insurance plans.

MassHealth, the state's Medicaid program for low-income individuals, automatically enrolled members in plans based on their primary care physician, so members should be able to keep their primary care doctors. But members may discover that as of March 1, their specialists are no longer in their insurance network or they have to use a new pharmacy.

The change is part of a move toward the use of "accountable care organizations," or ACOs, which are networks of providers that coordinate care and get paid for keeping a population healthy, rather than for each service.

"It's an enormous change," said Matt Klitus, chief financial officer and chief strategy officer for MassHealth. "We think it's an important change to get us to the point where there's appropriate accountability for the total cost of care, but no one should suggest this is a minor, trivial thing."

"This is a huge transition," Klitus added. "We need to be all hands on deck to make sure members get the care they need."

Massachusetts is spending $1.8 billion in new money over five years, half of that from the federal government, on this restructuring, which was conceived of in 2015.

Klitus briefed members of the Massachusetts Health Council, who represent a range of health care organizations, about the switch at a public meeting on Wednesday.

The move is expected to save money, although state officials could not provide an exact cost savings. In the first year, Klitus said it is expected keep the growth in annual per member payments by MassHealth to 2 percent, rather than the 3 to 4 percent it has been historically.

The goal is to better coordinate care for patients, to improve care and reduce hospital readmissions and emergency room visits. There is money for services that help people address problems that affect health like homelessness and food insecurity.

The state has authorized 17 ACOs. Around 800,000 to 850,000 people have been automatically enrolled in these new organizations, based on which one their primary care physician is affiliated with. If their physician did not join an ACO, the patient will remain with the doctor.

An estimated 300,000 to 400,000 MassHealth members are expected to remain in managed care or fee-for-service plans, which are the traditional MassHealth options. Members have been notified of the switch through a mailing.

Because each ACO works with a specific network of doctors, a patient's specialists might not be in the same network as their primary care doctor. So if a patient wants to keep seeing that specialist, the patient would have to switch networks. That could mean losing access to their primary care doctor. Primary care doctors can only participate in one ACO, while specialists can be in multiple networks.

"That will cause change and disruption," Klitus said. "We're doing our best to manage through the disruption."

To ease the transition, people will have a 30-day period after March 1 where they can still see their old doctors and use old authorizations to get medication. They will have 90 days where they can switch plans. Certain people will get longer transition periods, such as members who are pregnant or dealing with serious health problems.

There are standards to ensure the organizations provide high-quality care.

Several people in the health care industry said while they support the idea, they fear a difficult transition.

Dennis Lyons, a health care consultant who represents the Massachusetts Pharmacists Association, said many pharmacists do not know about the switch. "It's liable to be chaos," Lyons said.

Lyons said with 800,000 people automatically enrolled in plans they did not choose, many people will be moving from plans with freedom to access care anywhere to a restricted network.

Lyons worried that patients will show up at a pharmacy to get their medicine, but the pharmacy will no longer be in their network. The prescriptions would have to be transferred, and pre-authorizations would have to be reapplied for.

"This happens while the patient is standing there waiting for their medicine, and they're not going to get it ... unless everything is perfect," Lyons said.

Michael Tocco, president of Integrated Pharmacy Solutions, which represents 14 pharmacies in community health centers and hospitals, said, "I think new ways to try to manage cost and maintain quality are really important. However ... rolling it out in such a way that the providers don't get hurt is really a key issue."

Tocco said of his clients, "I know none of them have been informed as to exactly how they're going to be filling prescriptions within 10 or 12 days for a lot of clients."

Klitus said he is "concerned" that pharmacies have not been notified. Klitus said he is not expecting a "perfect" transition. "It would be naive to expect we have no disruption here," Klitus said. But, he said, "I am expecting the majority of issues are sorted out."

James Hunt, president and CEO of the Massachusetts League of Community Health Centers, said health centers have been working with patients to make sure the transition goes smoothly. He does worry that patients will show up at a health center and discover it is no longer in their network. The centers' policies are to treat everyone regardless of ability to pay, but the centers may not be able to get reimbursed by insurance.

Although MassHealth members have been notified, Hunt said, "We're talking about people who speak many different languages, people who may not understand the documents they receive."

"That will be a challenge, but we're up for that challenge," Hunt said. "We know new investments in primary care will allow us in the longer run to provide more comprehensive access to patients where they need it in communities rather than in emergency rooms."

Suzanne Curry, associate director of policy and government relations for Health Care for All, a health care advocacy group, said the group is continuing to run a helpline for consumers. MassHealth and the ACOs also have customer service.

Curry said so far, most calls have been from people trying to figure out if they can keep their primary care doctor and their specialists. "It is a big change," Curry said.

Curry encourages people to read the MassHealth mailing, figure out whether all their doctors are included in their new network, and determine what options they have for switching. Some people may end up with more plan options than they have today.

Curry said while MassHealth is trying to make the transition smooth, "we know some people will fall through the cracks," and Health Care for All will try to help those members.