The White House and Congress have done little to help. The Trump administration has imposed sharp cuts on the funding for outreach programs that assist people in signing up for coverage under the health law. And while House Democrats have passed legislation intended to help people to keep their health insurance, the bill is stuck in the Republican-controlled Senate.

Rather than expand access to subsidized insurance under the Affordable Care Act, Mr. Trump has promised to directly reimburse hospitals for the care of coronavirus patients who have lost their insurance. But there is little evidence that has begun.

“Helping people keep their insurance through a public health crisis surprisingly has not gotten much attention,” said Larry Levitt, executive vice president for health policy at the Kaiser Family Foundation. “This is the first recession in which the A.C.A. is there as a safety net, but it’s an imperfect safety net.”

The Families USA study is a state-by-state examination of the effects of the pandemic on laid-off adults younger than 65, the age at which Americans become eligible for Medicare. It found that nearly half — 46 percent — of the coverage losses from the pandemic came in five states: California, Texas, Florida, New York and North Carolina.

In Texas alone, the number of uninsured jumped from about 4.3 million to nearly 4.9 million; three out of every 10 Texans are uninsured, the research found. In the 37 states that expanded Medicaid under the Affordable Care Act, 23 percent of laid-off workers became uninsured; the percentage was nearly double that — 43 percent — in the 13 states that did not expand Medicaid, which include Texas, Florida and North Carolina.

Five states have experienced increases in the number of uninsured adults that exceed 40 percent, the analysis found. In Massachusetts, the number nearly doubled, rising by 93 percent — a figure Mr. Dorn attributed to a large number of people losing employer-based coverage there. Across the country as a whole, more than one in seven adults — 16 percent — is now uninsured, the analysis found.

To generate the estimates, Mr. Dorn examined the number of laid-off workers in each state and calculated how many had become uninsured based on coverage patterns since 2014, when the central provisions of the Affordable Care Act went into effect. The underlying data for those patterns comes from work published by the Urban Institute in April.