The share of people with health insurance fell last year for the first time since the Great Recession, according to data released Tuesday by the U.S. Census Bureau.

Approximately 27.5 million Americans, or 8.5% of the population, were without health coverage at some time last year, the data showed. That’s up from the 25.6 million Americans, or 7.9% of the population, in 2017. It’s the first annual increase since 2009.

The overall public health-insurance coverage rate declined by 0.4% to 34.4% of the population, while private health-insurance coverage rates, typically offered through an employer, remained steady at 67.3% of the population.

Researchers said government programs like Medicaid and Medicare are regarded as public coverage. Plans purchased through the federal marketplace established by the 2010 Affordable Care Act, counted as private coverage, the report added.

More children, ages 19 and under, lacked health-care coverage in 2018 compared to a year earlier.

Some 17.9% of Americans had Medicaid in 2018, a 0.7% drop in coverage, but Medicare coverage increased to 17.8%, a 0.4% increase. Medicaid provides public health insurance for people with low incomes who aren’t elderly. Medicare provides public health insurance for people aged 65 and older, and for some younger people with disability.

More children, ages 19 and under, lacked health-care coverage in 2018 compared to a year earlier: approximately 5.5% of America’s youth didn’t have health insurance, up 0.6% from the previous year.

Children from middle-class families experienced the biggest drop in health coverage: 2.6% of children from families making 400% above the poverty line — about $100,000 per year — lacked insurance last year, up 0.7% on the year.

Laryssa Mykyta, chief of the Census Bureau’s Health and Disability Statistics Branch, offered one theory. She said some children may have lost eligibility under certain state plans. Income eligibility for Medicaid varies by state.

Also Tuesday, the Census Bureau released data showing that the median household income climbed to $63,179, up from $62,626 a year earlier. The new rise, however, wasn’t statistically significant, census officials said. Median annual earnings for all workers rose 3.4% to $40,247.

As income levels rise, coinciding with a 10-year bull market and 3.7% unemployment, poverty levels have been falling: 11.8% of Americans were living in poverty last year, down from 12.3% in 2017. The official poverty rate hasn’t been this low since 2001, when it was 11.7%.