Coronavirus cases are surging in 15 states, a trend that’s worrying some experts, according to a new report.

Although the average U.S. case rate is falling overall — 32% in the last month — almost a third of all states have seen their average rate increase by at least 10%, according to ABC News. In six states — Delaware, Idaho, Minnesota, Nevada, Oregon and West Virginia — new case averages increased by at least 25% in the last week.

Two likely culprits are loosened public health restrictions and the spread of virus variants, industry observers say. 

“I don’t expect to see something as bad as we just recovered from, but if we’re not careful, cases can rise again if we let our guard down too soon,” epidemiologist Tara Smith, Ph.D., told ABC. 

Smith, of the Kent State University College of Public Health in Ohio, said she is most concerned about the effect of variant spread, and news of a recent outbreak in a Kentucky nursing home appears to confirm her fears. In that facility, a previously unidentified variant of COVID-19 had infected 27 residents, whether vaccinated or unvaccinated, and 14 staff members as of March 16.

Among those who were infected, 30% of those who were vaccinated had been symptomatic since testing positive. That’s in contrast with 83% of unvaccinated residents who showed symptoms after contracting COVID-19.

“Vaccination appears to have markedly reduced the risk of serious infection and hospitalization,” Kentucky Public Health Commissioner Steven Stack said in a press briefing. “Seventy-one people were vaccinated, one of whom is in the hospital. There were 13 residents unvaccinated, four of whom are in the hospital.”

It appeared that an unvaccinated person brought the variant into the building, he added.

Major urban areas are struggling with upticks linked to variants as well. In New York City, the U.K. and the New York variants now may account for most of the city’s cases, ABC reported.

“The best way to circumvent the variants is to continue to vaccinate as many people as quickly and as efficiently as possible at the same time as maintaining your public health measures,” Anthony Fauci, M.D., the White House’s chief medical adviser, told the news outlet.

The 15 states with surges include Alaska, Connecticut, Delaware, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Nevada, New Hampshire, New Jersey, Oregon and West Virginia, according to an ABC analysis of federal data.

Additional reporting by Kimberly Marselas, senior editor of McKnight’s Long-Term Care News.