Cases are rising in nearly every corner of the United States.

Coronavirus cases and hospitalizations are rising in a majority of American states, in what appears to be the first widespread increase since the peak of the Omicron surge in January.

Reports of new cases were nearly flat in the United States at the beginning of April, but as the month draws to a close, they are increasing in all but three states, signaling a wave that is increasingly national in scope.

“Most of the cases are relatively mild,” said Dr. Eric S. Toner, a senior scholar at the Center for Health Security at the Johns Hopkins Bloomberg School of Public Health.

The recent increase was once concentrated in the Northeast, but the effects of the highly contagious BA.2 subvariant is growing more geographically diverse. In the last two weeks, cases have more than doubled in states from West Virginia to Utah.

Hospitalizations are also on the rise nationwide, after plummeting early this month to their lowest point since March 2020. More than 30 states and territories have seen their hospitalization rates tick up in the past two weeks, and in much of the Northeast, the number of people hospitalized with the coronavirus has increased since mid-month by 40 percent or more.

“It’s not over yet,” Dr. Toner said in an interview on Friday. “It may be a mistake to relax all of our protective measures too quickly.”

Still, new data from the Centers for Disease Control and Prevention shows that more than 60 percent of Americans have been infected with the coronavirus at least once, lending credence to the belief that the modest effects of this surge could reflect growing immunity from previous infections and vaccinations.

The number of new cases announced each day in the United States — about 55,000 — remains at its lowest level since last summer, and hospitalizations, despite recent growth, are still nearly as low as they have been at any point in the pandemic.

Case counts have become an increasingly unreliable measure of the virus’s true toll, as Americans increasingly turn to at-home tests that go unreported. That has prompted some officials to put more emphasis on hospitalization rates as a measure of the virus’s true impact.

“What we’re not seeing is a lot of stress on hospitals, and that’s very encouraging,” Dr. Toner said.

Fewer than 400 coronavirus deaths are being reported each day in the United States, the lowest daily average since before the Omicron variant took hold late last fall. Deaths have decreased by more than 20 percent in the last two weeks. In the past, however, trends in deaths have lagged behind cases and hospitalizations by weeks because of the time it takes for people to become seriously ill, and the time needed to complete and file death records.

The country’s current hot spot is in central New York, where nearly all the counties have “high” community levels of the coronavirus, according to the C.D.C. The region includes cities like Binghamton, Buffalo, Rochester, Syracuse and Utica.

“It is clear that Covid is here, and will be here for some time,” Dr. Toner said. “Some degrees of caution is wise if one is at elevated risk and in a crowded place. Doing things like wearing a mask still make a lot of sense.”