About 16.4 million adults have been added to health insurance rolls under the Affordable Care Act, which provided especially robust gains in coverage for minorities and states that expanded their Medicaid programs, administration officials announced Monday.

The total includes 14.1 million adults who joined the insurance rolls since October 2013 and 2.3 million younger adults ages 19 to 25 who were able to remain on their parents’ health insurance plans since October 2010, when that provision of Obamacare went into effect.

Richard Frank, the assistant secretary for planning and evaluation at the Department of Health and Human Services, called the gains “historic,” comparing the impact to the creation of Medicare and Medicaid in the mid-1960s.

HHS Secretary Sylvia Mathews Burwell said she was “pleased” with the numbers but added that the government still can enroll greater numbers of African Americans and Latinos.

“African American, Latino [rates] are not exactly where you want to be, because the [uninsured] numbers are still high,” Burwell said. “I believe we can do more.”

Obama administration officials announced on March 16 that about 16.4 million adults have been added to health insurance rolls under ACA. (Karen Bleier/AFP/Getty Images)

The Latino uninsured rate dropped by 12.3 percentage points between the first quarter of 2014 and the same period in 2015 as 4.2 million adults gained coverage. That ethnic group, however, continues to have the lowest rate of insurance coverage.

About 2.3 million African Americans enrolled, dropping that group’s uninsured rate by 9.2 percentage points, and 6.6 million whites obtained coverage, a decline of 5.3 percentage points.

The data are based on surveys conducted for HHS. The totals do not show whether an individual obtained coverage through the new insurance marketplaces, a private employer or some other method. No numbers on children were included.

States that decided to expand their Medicaid insurance programs for the poor recorded bigger gains than those that didn’t, reducing their uninsured rate by 7.4 percentage points as compared with 6.9 points for states that declined to expand.

Meena Seshamani, director of HHS’s Office of Health Reform, said the 16.4 million newly covered adults no longer need to put off health care “because they can’t afford it” or “worry about going broke” if they face a serious illness.

“Today’s news is good for the health and financial security of millions of Americans,” she said.

Juliet Eilperin contributed to this report.