For the second year in a row, New Hampshire and the U.S. experience a rough flu season

Epidemiologist at Dartmouth Hitchcock Medical Center in Lebanon. Michael Calderwood said this flu season was “probably the third most severe among adults” in recent history.

America Centers for Disease Control and Prevention According to the most recently available data, at least 37 million cases of influenza, 370,000 hospitalizations, and 23,000 deaths are estimated to have occurred in the United States this season as of March 28. In New Hampshire, 71 people have died from influenza, according to New Hampshire Department of Health and Human Servicesincluding two children. The CDC currently rates New Hampshire as having a “moderately severe” influenza level. The state’s neighbor to the south, Massachusetts, is also classified as “moderately severe” but Vermont has “minimum” levels and Maine has “low” levels.

The 2025-26 season follows 2024-25, which Calderwood said was the worst flu season since 2011, especially for children. In the 2024-25 season, 289 children died of influenza across the country. 123 children have died so far this flu season. He cautioned that “the numbers are still coming in, so we don’t have final estimates for this year.” The typical flu season runs from early October to mid-May.

Calderwood said December was particularly bad, with hospitals challenged to keep going. This year’s peak was New Year’s week – two weeks before last year’s peak – and then it started to taper off. Most of that increase, Calderwood said, was influenza A, but he said influenza B still circulates in March and April. Influenza B figures are now almost twice as high as this time last year.

There were 5,701 positive influenza B tests reported (82.5% of all influenza cases) in the week ending March 21 and 72,175 throughout the season, according to the CDC. Last year there were 3,397 influenza B tests (40.6% of all cases) in the week ending March 22, 2025, and 32,218 at that point in the season.

Calderwood said this season has been particularly bad for childhood influenza cases, which have taken a toll on schools.

“What was strange this year was that the flu caused a lot of GI illness,” he said. “So schools were seeing more kids going home with vomiting and diarrhea, more than just common respiratory illnesses.”

What’s more about him is that doctors are seeing an increase in influenza-related acute necrotizing encephalopathy.

“It’s a big, fancy name,” he said. “But what it really means is that brain swelling is an immune response that gets out of control. And 1 in 4 people who come down with it die. And of those who survive, about two-thirds are left with some degree of disability. And that’s vaccine preventable.” Calderwood believes that new strains are more likely to affect this trait.

Calderwood suspects that the driver behind the difficult back-to-back flu seasons is low vaccination rates and a vaccine that didn’t match up well with this year’s newest strain of the virus. As of Feb. 22, an estimated 46.5% of American adults reported receiving this year’s flu shot, according to CDC. He said the nation’s epidemiology community has set a goal of reaching 70 percent vaccination rate by 2030.

“In 2024-2025, vaccines accounted for 10 million symptomatic illnesses, 5 million medical office visits, 180,000 hospitalizations, 12,000 deaths,” he said. “So vaccines have a big impact. At the same time, we saw a 5% drop in kids getting vaccinated that season. And that’s a pretty big number when you think about that drop off.”

He encourages parents to get their children vaccinated against influenza starting at 6 months, when they are first eligible for shots.

“That’s where we’re seeing a massive decline,” he said. “And that’s the group that’s at the highest risk of death.”

But he recommends getting the vaccine for adults as well.

“We have very effective vaccines, very safe vaccines,” he said. “And so understanding that that protection is something worthwhile, both to protect themselves but also to protect the people around them, especially those who may have an age or an immune system that means they know, they won’t have as much protection.”

The elderly, infants, and those with medical conditions that affect their immune systems are most at risk for more severe flu symptoms.

Calderwood believes that next year, epidemiologists will be able to better match the vaccine to the new strain of the virus.

The CDC has been rocked by mass layoffs since President Donald Trump took office in January 2025, but Calderwood said he’s “impressed with the data we keep getting.”

“There are certain areas where we don’t have this robust data,” he said. “Covid tracking is one of them. But really, there’s kind of a robust infrastructure for tracking respiratory viruses nationally, so our flu data, our RSV data, continues to be something we can trust.”

As for his clinic in Lebanon, Calderwood said he sees a mix of concerns among his patients. Some are very concerned, wear masks, and want to do what they can for prevention “and you have others kind of scoffing that we need to do something about prevention. And really it’s very divisive.”