Across the United States, officials have dropped mask mandates and are closing mass vaccine and testing sites as new coronavirus cases have fallen nationally to about 27,000 a day on average. But several states — mostly in the Northeast — have had some increases in case numbers over the past two weeks, according to a New York Times database.

Though their average number of new cases remains much lower than during the winter omicron surge, New Jersey, New York, Massachusetts and Connecticut have seen cases jump by more than 40% over the latest 14-day period as of Saturday, according to the Times database.

Some other states have also seen slight upticks in new cases over the past two weeks, including Illinois (13%); New Hampshire (19%); Delaware (17%); Wisconsin (11%); and Florida (25%), the Times database shows.

Those shifts come as the highly transmissible omicron subvariant known as BA.2, which had led to cases increasing in Europe, became the dominant version of the coronavirus among new cases in the U.S., according to federal estimates last week. BA.2 is similar to the form of omicron that recently swept the U.S. over the winter.

“We are in a watch-and-see period, unfortunately, because so many states have removed mitigation, and so many people are fatigued by said mitigation,” Bertha Hidalgo, an associate professor of epidemiology at the University of Alabama at Birmingham, said when asked recently about the current state of the pandemic in the U.S.

Some U.S. health officials have said they expected case numbers to rise without a major surge caused by BA.2, though at-home test results are not always officially reported. Still, other scientists worry that the nation isn’t doing enough to prevent another possible surge.

“Cases are ticking up as we thought they might,” President Joe Biden said last week as he called for Congress to approve stalled emergency aid, adding that “Americans are back to living their lives again. We can’t surrender that now.”

But Senate Democrats and Republicans were nearing an agreement that would slash the COVID-19 response package to $10 billion, from $15.6 billion.

Hidalgo said that a new surge could potentially increase hospitalizations in some parts of the country, particularly in places where a majority of eligible people have not received a booster shot of a coronavirus vaccine. Federal health officials cleared second boosters for some people last week, and scientists have cautioned that future variants may be better able to sidestep our defenses.

“We cannot be cavalier about this virus,” Hidalgo said, adding, “We need mitigation, a push for vaccination and overall a preventive approach instead of a reactive approach to prevent additional cases this time.”

Vaccines continue to protect against the worst outcomes, but only about 60% of Americans older than 65 have had a first booster shot, according to federal data. That leaves many people vulnerable, said Dr. Jeffrey Klausner, a professor of medicine at the University of Southern California, though the emergence of new treatments, such as an antibody drug for people with weakened immune systems, and antiviral pills, kept him optimistic.