New health insurance options made available by the Affordable Care Act have cut the percentage of uninsured Californians by half – the sharpest reduction by far among the six largest U.S. states, according to a survey released Thursday.

The survey, conducted by the New York-based Commonwealth Fund, shows that California’s uninsured rate dropped from 22 percent last summer to 11 percent as of early last month. Driving the change were higher-than-expected enrollment in subsidized health plans through Covered California, the state-run insurance exchange, and an expansion of Medicaid, the government insurance program for low-income people.

Nationwide, the percentage of the population without health insurance declined from 20 percent to 15 percent over the same period, according to the survey, which polled 4,425 adults between April 9 and June 2.

That is in line with a Gallup survey published last month that showed the U.S. rate of uninsurance falling from 18 percent in the third quarter of 2013 to 13.4 percent in the second quarter of this year.

Among people newly enrolled in health plans through insurance exchanges or Medicaid, nearly two-thirds were previously uninsured, according to the survey.

“The findings suggest that the Affordable Care Act is beginning to achieve its central goal – reducing the number of Americans who are uninsured and improving access to health care,” said Sara Collins, a Commonwealth Fund vice president who headed the survey.

The analysis accompanying the survey results tied California’s success to the fact that it was the first state to establish its own insurance exchange under the Affordable Care Act, also known as Obamacare.

And, unlike some other large states, it embraced Obamacare’s proposed – but not required – expansion of Medicaid, known in California as MediCal.

In addition, California health officials “pursued an aggressive outreach and enrollment campaign over the first enrollment period” from Oct. 1 to March 31, the study said.

The new estimate of California’s uninsured population “is a very credible number,” said Shana Charles, director of health insurance studies at UCLA’s Center for Health Policy Research.

“California has had an incredible amount of success,” said Charles. “We were enrolling people at a fast and furious pace, and we are showing the results.”

Covered California signed up 1.4 million people in the six-month Obamacare enrollment period – double its most optimistic forecast. It predicted that about 85 percent of those, or 1.2 million, would complete the enrollments by actually paying their premiums.

Another 2 million Californians signed up for MediCal, and hundreds of thousands more are waiting for their enrollments to be processed.

In Texas and Florida, which rejected the Medicaid expansion and sent residents to the problem-plagued federal insurance exchange, the rate of uninsurance remains stubbornly high – 22 percent and 26 percent, respectively, according to the Commonwealth Fund. However, the rate in Texas is well below last summer’s 34 percent level, thanks to stronger-than-expected signups through the federal exchange.

A modest drop in Florida’s uninsurance rate “was not statistically significant,” the study said.

Nationwide, the rate of uninsurance among Latinos dropped from 36 percent to 23 percent, according to the survey. Among young adults, it dropped from 28 percent to 18 percent.

In California, where Latinos make up nearly two-thirds of the uninsured population, they accounted for 28 percent of enrollees in Covered California health plans. The exchange was hamstrung in its early outreach efforts to the Latino community by not having enough bilingual enrollment counselors. Also, it failed for the first several months to produce a Spanish-language application.

Though signups of young people surged in the past month, their share of total enrollment is well below Covered California’s ultimate goal of closer to 40 percent.

The Commonwealth survey also showed that, despite frequent complaints about slim pickings of doctors and hospitals among exchange-brokered health plans, more than half of those surveyed said that some or all of their doctors were covered by the policies they purchased.

More than 60 percent of those who selected primary care doctors were able to get appointments within two weeks, and 81 percent of people newly enrolled in health plans said they were optimistic that their insurance would improve their ability to get the care they needed.

“It shows that people of all stripes and colors are finding a product that works for them with the options available,” said UCLA’s Charles. “ And I think that’s very good news.”

Contact the writer: 714-796-2440 or bwolfson@ocregister.com