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After a dramatic decline since mid-January, COVID-19 cases are rising again in New Hampshire.

The state averaged 329 new cases per day for the week ending Thursday — up 37 percent from March 6, when the seven-day average hit a low of 240. The percentage of tests coming back positive has drifted up as well, hitting an average of 4.4 percent for the week ending Wednesday.

Cases remain far below their peak in December and January, when they sometimes averaged more than 800 per day. But the recent uptick is something health experts had warned about as cases declined, saying that relaxing public-health measures amid the spread of more contagious variants could reverse that progress.

“We are not yet out of the woods, mask use and social distancing is still essential, travel should be limited, and everyone without a contraindication” — a condition that raises the risk of an adverse reaction from the vaccine — “should step forward to be vaccinated as soon as it is available to them,” Dr. Michael S. Calderwood, an infectious disease physician and the chief quality officer at Dartmouth-Hitchcock Medical Center in Lebanon, said in an email Friday.

A steep decline in new cases in January and February, followed by a plateau and recent rebound, mirrors national trends.

Calderwood cited several national statistics indicating that compliance with public health precautions may be slipping.

The percentage of Americans who say they always wear a mask in public has ticked down three percentage points since peaking at 78 percent on Feb. 12, according to survey data. Cellphone mobility data show Americans are moving around more than a month ago. And air travel recently hit its highest point since the pandemic began.

Dr. Aalok Khole, an epidemiologist with Cheshire Medical Center in Keene, said he doesn’t know exactly why cases have gone up in New Hampshire, but suggested some possible factors.

Outbreaks on college campuses, increased travel and, perhaps, more people out and about as the weather warms “may have led to some dropping their guard and failing in conservative measures like hand hygiene, mask compliance and physical distancing,” he said by email.

Khole noted that the cases are largely in people under 60, “so not in the group that has been extensively vaccinated.”

It’s unclear how much new COVID-19 variants have played into the rise locally, Khole said. More than 50 cases of the more contagious B.1.1.7 variant, first identified in the United Kingdom, have been detected in New Hampshire, according to the most recent count from the Centers for Disease Control and Prevention. While the state has no known cases of either the B1.351 or P.1 strains — first found in South Africa and in four travelers from Brazil on their arrival in Japan, respectively — both have been identified in Massachusetts.

“We are testing more for these variants now compared to back in Jan 2021 — both within NH and across the US,” Khole said. “… But we still aren’t testing as much as we should be.”

Meanwhile, the number of hospitalized patients appears to have plateaued in New Hampshire, fluctuating between 63 and 82 in the past two weeks — though far below the peak of more than 330 in early January, and “nowhere close to overwhelming healthcare facilities,” Khole said.

Still, both Khole and Calderwood pointed to the ever-increasing number of vaccinations as a reason for optimism. With much of the most vulnerable population vaccinated, Khole said, the state is seeing far fewer deaths than it was a couple months ago.

As of Friday, more than 350,000 Granite Staters had received at least one dose of a vaccine, of whom 200,000 are fully vaccinated — meaning more than a quarter of the state’s population has now been at least partly inoculated, according to data from the N.H. Department of Health and Human Services. And on Thursday, Gov. Chris Sununu announced that any adult who wants a vaccine will be eligible to sign up by the end of this coming week.

“I think the best ray of hope is increasing number of vaccinations per day and further groups becoming eligible for the shot,” Khole said. “This is our ticket out of this pandemic and we need everyone to get on board.”

Paul Cuno-Booth can be reached at 352-1234, extension 1409, or pbooth@keenesentinel.com. Follow him on Twitter @PCunoBoothKS