Cases rise due to strain and low vaccination

Local doctors say a perfect storm has developed, a rapidly spreading strain of influenza A compounded by a drop in vaccination rates and an increase in holiday travel, which could elongate the flu surge into spring.

“This is one of those seasons where everything is lining up in the wrong direction,” said Dr. Vandana Madhavan, clinical director of infectious disease at Mass General Brigham for Children. “It’s hard to say when our peak is going to be, and in some years, we see a second peak.”

At the end of December, the number of visits to health care providers for flu-like illness jumped to 11.8 percent, up from 7.6 percent the week before, according to the Massachusetts Department of Public Health. The share of emergency room visits that resulted in a hospitalization for influenza rose to 9 percent — nearly double from the previous week and triple the rate from the same time last year.

Each day last week, there were nearly 9,000 emergency department visits statewide, with about one-quarter of those related to acute respiratory illness, including flu, COVID-19, and RSV, or respiratory syncytial virus.

Last year, flu hospitalizations in Massachusetts peaked in early February, when about 10.5 percent of hospital admissions were attributed to influenza. This year’s trajectory suggests the state could meet or surpass that mark, said Dr. Larry Madoff, of the Massachusetts Department of Public Health.

“The flu season is likely to continue well into the spring. Typically, it doesn’t peak until late January or February,” said Madoff, medical director of the department’s Bureau of Infectious Disease and Laboratory Sciences.

Starting Tuesday, Brown University Health will require surgical masks or N95s for all patients, visitors, and staff at all times across its locations in Massachusetts and Rhode Island due to high rates of hospital infections.

Nationally, the picture is similarly grim. Through Dec. 27, the Centers for Disease Control and Prevention reported “very high” flu activity in more than half the states. The agency estimates there have been at least 11 million illnesses, 120,000 hospitalizations, and 5,000 deaths so far this season, including at least nine children nationwide.

In the state, 32 influenza-related deaths have been reported this season — 29 adults and three children, including one child who died during Christmas week. Last season, which ran from fall to summer, there were 470 influenza-related deaths. The state is also reviewing two possible COVID-19-associated deaths and one RSV-associated death in individuals younger than 18 years.

Influenza is a contagious viral illness that attacks the respiratory system, including the nose, throat, and lungs. Typical symptoms include high fever, cough, sore throat, body aches, and extreme fatigue, sometimes accompanied by nausea, vomiting, or diarrhea. This season, clinicians are reporting fevers as high as 104 or 105 degrees in some patients.

Doctors say the intensity of this year’s outbreak is driven by a dominant strain of influenza A H3N2 — specifically, a genetic variant known as subclade K.

Among influenza A H3N2 viruses that have undergone further genetic analysis at the CDC, about 90 percent belong to subclade K. While experts are still studying whether it causes more severe disease, early evidence suggests it spreads more quickly and may be better at evading existing community immunity.

Internationally, subclade K has already raised alarms. Health leaders in the United Kingdom warned in November of a “once-in-a-decade” winter flu surge as infections rose sharply among young people. The strain has also been detected in Canada and Japan, where authorities declared a flu epidemic as early as October.

“It really did feel like a switch flipped,” said Dr. Zachary Binder, an associate professor of pediatrics at UMass Chan Medical School and a pediatric emergency medicine physician at UMass Memorial Medical Center in Worcester. “We went from seeing hardly any flu to over half the patients in the emergency department being flu positive.”

Binder said more than half the patients he treated in recent weeks had influenza A, and many children experienced febrile seizures triggered by dangerously high fevers.

“We are seeing an absolute explosion in flu cases over the last few weeks,” Binder said. “When we see kind of severe cases, even death, it’s most often in children with underlying health conditions like asthma, other respiratory illnesses, or cardiac illnesses.”

Another major factor is the lack of vaccination. Only about 34 percent of Massachusetts residents have received a flu shot so far this season, according to the state’s tracker. That’s a drop from last year, when roughly 40 percent of residents were vaccinated.

Complicating matters further, the newly mutated strain, which was surging earlier in the UK, appears to be only a partial match to this year’s vaccine. Each year, scientists must predict which flu strains are most likely to circulate months in advance, and this year’s prediction missed the mark.

Madoff, of the state’s Department of Public Health, said even though the circulating strain “is not a perfect match for the vaccine, a vaccine is far better than no vaccine.”

He said it’s unfortunate that more people are choosing not to vaccinate in the state, and combats the federal health officials’ decision Monday to slash recommended childhood vaccinations under President Trump’s directive.

“I think it’s the wrong move at the wrong time,” Madoff said. “It flies in the face of what doctors recommend and what our professional organizations recommend. This guidance seems to backtrack on important protections for our children, and backing off on those recommendations, weakening those recommendations in any way, is exactly the wrong thing to be doing.”

The reasons for declining flu vaccination rates are complex. Some experts point to pandemic fatigue such as reduced routine care visits, and lingering skepticism about vaccines following COVID-19. Others note that people may underestimate the severity of influenza compared with other respiratory viruses.

Still, physicians in Massachusetts stress that the vaccine significantly reduces the risk of severe illness, hospitalization, and death.

“It does take a couple of weeks to get full protection from vaccination,” Madhavan said. “Now is the time, if you haven’t gotten vaccinated, to get vaccinated, to get some protection on board. And I would say that for COVID as well.”

Pediatric specialists say they are seeing more severe complications in children than usual. Madhavan, with Mass General Brigham for Children, said she has treated patients with acute necrotizing encephalopathy, a rare but serious complication of influenza that can cause sudden changes in mental status, difficulty speaking or eating, problems with movement, and, in severe cases, trouble breathing.

Severe flu cases are more common in children with underlying health conditions, but even otherwise healthy children can become critically ill, doctors warn. Parents are urged to watch for signs of dehydration, difficulty breathing, persistent high fever, or lethargy.

For home care, Madhavan recommends aggressive hydration, including popsicles and electrolyte solutions like Pedialyte, along with controlling fever using ibuprofen or acetaminophen. Honey can help soothe coughs in children older than 1, she recommends.

COVID-19 activity in Massachusetts remains relatively low compared with influenza, though health officials caution that seasonal waves can overlap.

For now, doctors and public health officials are urging residents to get vaccinated, stay home when sick, wash hands frequently, and seek medical care early if symptoms worsen.

Madoff recommends residents seek care as soon as symptoms onset.

“There are treatments available, and the earlier those treatments are started, the more beneficial they are,” he said. “For the vulnerable populations like young children, older adults, those with underlying medical conditions, those with respiratory issues or cardiovascular issues, Tamiflu and other treatments can be lifesaving.”

Sarah Rahal can be reached at sarah.rahal@globe.com. Follow her on X @SarahRahal_ or Instagram @sarah.rahal.