When Massachusetts passed its landmark health insurance law under Gov. Mitt Romney in 2006, no one claimed the state would get to zero — as in 0 percent of residents who are uninsured. But numbers out this week suggest Massachusetts is very close.

Between December 2013 and March of this year, the number of Massachusetts residents signed up for health coverage increased by more than 215,000. If that number holds true over time, it will mean the percentage of Massachusetts residents who lack coverage has dropped to less than 1 percent.

"We're thrilled that we are getting this close to universal health care access," said the Rev. Burns Stanfield, president of the .

Stanfield says the strong numbers — especially when coupled with last month's finding that mortality rates dropped in the first four years of expanded coverage in Massachusetts — show that "our statewide move to universal access is working, and it's a powerful witness to the nation."

But that kind of enthusiasm is not coming from state officials — yet.

"These numbers are a sign that we are moving in the right direction, but there is still a lot of uncertainty about what they will ultimately mean to the total level of health insurance coverage in Massachusetts," says Áron Boros of the Center for Health Information and Analysis, the state agency that tallied the latest insurance figures.

Uncertainty might be an understatement. There is still a tremendous backlog of applications to process. Most of the new enrollees are in a temporary coverage plan because the state, with its failed website, has not been able to figure out if these people qualify for free or subsidized care.

What if they don't qualify for help, asks Lora Pellegrini, president of the Massachusetts Association of Health Plans. Will these new enrollees be willing to pay what could feel like a hefty premium?

"The real challenge," Pellegrini says, "is going to be to move these folks from the temporary coverage into the permanent coverage where they belong, and then see if we're able to retain these numbers."

There are reasons to think the numbers may hold. Despite the state's broken website and confusion about deadlines and eligibility, it looks like more than 200,000 Massachusetts residents who did not have health insurance last year managed to enroll.

There are some good explanations for why:

First, there was a big federal enrollment campaign in the fall and spring that might have caught people's attention.

Second, more residents are eligible for free coverage or subsidized help with premiums under the new federal insurance law.

Third, most of those who were still uninsured in Massachusetts at the end of 2013 were low-income workers who could not afford premiums under an employer's plan. Under the previous Massachusetts health care law (enacted under then-Gov. Mitt Romney), workers were not allowed to sign up for state-subsidized insurance if they had access to a health plan through work. The federal law lifts that restriction.

"It is hard not to look at this and say, if it turns out the numbers are actually correct — that's a big if — this is good," said , a senior fellow at Project Hope and a former health care adviser to President George H.W. Bush. "It is urgent that we have confirmation that continued enrollment after the first year can happen and, in fact, in a place like Massachusetts did happen."

The state may be dropping even closer to zero than the numbers released this week indicate because of movement in the coverage market. The analysis reflects March numbers when 167,000 residents were in temporary coverage; but as of this week, Gov. Deval Patrick's office says there are 217,000 in that plan. It's not clear how many of these people are newly insured. Private health insurers lost at least 10,000 members during the first quarter of this year.

Massachusetts will continue to have some undocumented residents and others who lack health insurance. Making sure coverage is affordable is an ongoing challenge, and subsidizing insurance for more residents could strain the state budget. But for now, it looks as though Massachusetts is the first state in the country where nearly everyone can focus more on their health — and less on whether they'll be able to see a doctor — if they become injured or ill.

This story is part of a reporting partnership with NPR, WBUR and .

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