Millions of Americans could temporarily be left without insurance coverage under the recent health care reform legislation, according to a study co-authored by Benjamin D. Sommers, an assistant professor at the Harvard School of Public Health.

Singed into law by President Obama last March, the health care reform legislation seeks to provide affordable coverage for all Americans.

But according to Sommers, under the new law, monthly fluctuations in income will cause low-income families to move back and forth between Medicaid and subsidized insurance coverage obtained through federally-mandated state exchanges. Some people may have to wait several weeks after their Medicaid coverage ends for their exchange insurance to take effect or vice versa, Sommers said.

According to the report, more than 35 percent of all adults with family incomes below 200 percent of the federal poverty level will experience a shift in eligibility from Medicaid to an insurance exchange. Within 50 years, 28 million people will have undergone the same shift.

“Some of the people who would benefit the most from health care reform are people who stand to gain an enormous amount but are going to have challenges remaining continuously insured and with continuity of care,” said co-author Sara Rosenbaum, a law professor at George Washington University.

The researchers began investigating the topic for their study last summer by obtaining income and insurance status data from Survey of Income and Program Participation, a national survey administered every four months by the Census Bureau.

From this, Sommers said they determined who would initially qualify for Medicaid or state exchanges under health care reform and then tracked every time low-income families crossed the threshold between Medicaid and exchange eligibility each month.

Sommers said the “bouncing around” of incomes on a monthly basis was more common than he initially thought.

“It does look like this is really going to be an issue states are going to have to address if they want to minimize disruptions,” Sommers said.

Though coverage disruption is not a new issue—and the act does provide some safeguards for families experiencing a change in income—the report offers several suggestions to facilitate the transition between insurance policies. Policy options include reducing the likelihood of frequent eligibility changes, providing support services for the shift, and aligning coverage and benefits.

The new health care law is the largest expansion of health coverage for lower-income people since the enactment of Medicare and Medicaid in the 1960s, according to the report.

“This will still be a major improvement for their health care access compared to now, since millions of these adults currently have no insurance at all,” Sommers said. “But our study points out that state and federal policy makers will need to take steps to reduce the frequency of coverage changes for these families and to protect the continuity of their health care.”

—Staff writer Melanie A. Guzman can be reached at melanieguzman@college.harvard.edu.