In late December 2025, Massachusetts clinicians reported a sudden and widespread rise in influenza cases, attributing the surge to a fast-spreading H3N2 variant, falling vaccine uptake, and increased holiday travel. State data showed outpatient visits for influenza-like illness climbed to 11.8 percent at the end of December, up from 7.6 percent the prior week, while emergency-department visits resulting in influenza hospitalizations rose to about 9 percent. Hospitals across the state logged nearly 9,000 emergency visits per day last week, with roughly one-quarter related to acute respiratory illness. Physicians warn the wave could extend into spring and possibly reach or exceed last season’s hospital burden.
Key takeaways
- Outpatient visits for flu-like illness in Massachusetts rose to 11.8% the week ending late December, up from 7.6% the previous week (Massachusetts DPH).
- ER visits that led to influenza hospitalizations increased to approximately 9% statewide — nearly double the prior week and three times the rate at the same time last year.
- Daily statewide emergency-department visits were close to 9,000 recently, with about 25% for acute respiratory conditions including flu, COVID-19, and RSV.
- The dominant circulating strain is influenza A H3N2, with about 90% of genetically characterized H3N2 viruses at the CDC classified in subclade K.
- Vaccination coverage in Massachusetts is low this season at roughly 34%, down from about 40% last year, leaving more people vulnerable.
- National CDC estimates through Dec. 27 report at least 11 million illnesses, 120,000 hospitalizations, and 5,000 deaths this season; Massachusetts reported 32 influenza-related deaths so far (29 adults, 3 children).
- Brown University Health implemented a requirement for surgical masks or N95s for patients, visitors, and staff across its Massachusetts and Rhode Island sites due to high hospital infection rates.
Background
Influenza activity typically rises in late fall and can peak between late January and February. Public-health surveillance combines outpatient visit percentages, emergency-department trends, hospitalization rates, and lab-based genetic analyses to identify circulating viruses and gauge severity. After two seasons shaped by COVID-19, routine care and vaccination attendance have not fully returned to pre-pandemic norms, and health officials cite that as one factor in lower flu-shot uptake this year.
With influenza A H3N2 dominant, this season differs from years when H1N1 or influenza B have led. H3N2 seasons historically produce higher hospitalization and complication rates among older adults and young children. Healthcare systems brace for elevated pediatric and adult admissions when a fit between the circulating strain and the seasonal vaccine is suboptimal, as appears to be the case this year.
Main event
Clinicians across Massachusetts began noting a rapid increase in flu-positive tests in recent weeks. Emergency departments that had seen few influenza cases early in the season reported a dramatic shift: more than half of some pediatric ED patients recently tested positive for influenza A, according to pediatric emergency physicians. High fevers — reported in some patients at 104–105°F — led to febrile seizures in several children.
State surveillance at the end of December recorded a jump to 11.8% of visits for influenza-like illness and an ER-to-hospitalization rate for influenza near 9%. By comparison, last season’s peak hospitalization share was about 10.5% of hospital admissions in early February, a level state officials say this season may match or exceed if trends continue.
Clinicians point to three converging drivers: a rapidly spreading genetic subvariant of H3N2 (subclade K), a measurable decline in seasonal influenza vaccination rates (34% vaccinated so far in Massachusetts), and increased travel and gatherings over the holidays that accelerate transmission. Local medical centers reported more severe pediatric complications than typical, including rare conditions such as acute necrotizing encephalopathy in isolated cases.
Analysis & implications
The predominance of H3N2 subclade K has international precedents: public-health officials in the U.K., Canada, and Japan reported early and intense H3N2 activity in autumn and winter 2025–26. Genetic surveillance by the CDC shows roughly 90% of analyzed H3N2 viruses fall into subclade K, suggesting the variant is broadly seeded in U.S. communities. Early indicators point to faster spread; whether K increases intrinsic severity is still under study.
Lower vaccination rates amplify risk. Even when a vaccine is not a perfect antigenic match, it commonly reduces severe outcomes, hospitalizations, and deaths. State officials stressed that incomplete vaccine coverage limits community protection and leaves higher-risk populations — young children, older adults, and people with chronic conditions — more exposed.
Healthcare capacity is vulnerable to sustained respiratory surges. Nearly 9,000 ED visits per day and a high share for respiratory complaints strain staffing and bed availability, especially if influenza hospitalization percentages approach or surpass last season’s 10.5% admission share. Schools and pediatric clinics face pressure from higher pediatric illness and complications, which can in turn drive absenteeism and secondary impacts on families and workplaces.
Comparison & data
| Measure | This season (late Dec) | Approx. prior season peak |
|---|---|---|
| Outpatient visits for ILI | 11.8% (week ending late Dec) | Varied; typically lower early in season |
| ER visits leading to influenza hospitalization | ~9% | ~5% (similar week last year) |
| Hospital admissions attributable to influenza (peak) | — (trajectory suggests up to ~10.5%) | ~10.5% (early Feb, prior season peak) |
| State flu vaccination rate | ~34% | ~40% (last season) |
| CDC U.S. burden (through Dec. 27) | 11M illnesses, 120K hospitalizations, 5K deaths | N/A |
The table above collates key surveillance snapshots. While weekly numbers fluctuate, the convergence of high outpatient ILI shares, rising hospitalizations, and low vaccination coverage creates a higher likelihood that the season’s burden will exceed routine expectations. Public-health leaders monitor both viral genetics and clinical severity to refine recommendations.
Reactions & quotes
State and clinical leaders emphasized caution and prevention while noting available treatments can reduce severe outcomes when started early.
“This is one of those seasons where everything is lining up in the wrong direction.”
Dr. Vandana Madhavan, Mass General Brigham for Children (clinical director, infectious disease)
Dr. Madhavan highlighted pediatric complications and urged vaccination and early care-seeking, saying aggressive home hydration and fever control remain key initial measures.
“The flu season is likely to continue well into the spring. Typically, it doesn’t peak until late January or February.”
Dr. Larry Madoff, Massachusetts Department of Public Health (medical director, Bureau of Infectious Disease and Laboratory Sciences)
Madoff stressed that even a partially mismatched vaccine offers meaningful protection and urged adherence to professional immunization guidance amid policy changes at the federal level he described as ill-timed for this season.
“We went from seeing hardly any flu to over half the patients in the emergency department being flu positive.”
Dr. Zachary Binder, UMass Chan Medical School (associate professor of pediatrics)
Binder described the sudden influx of influenza-positive patients and noted severe cases, including febrile seizures in children, were concentrated among those with and without underlying conditions.
Unconfirmed
- Whether subclade K causes intrinsically more severe illness than previous H3N2 variants remains under investigation; current genetic data show rapid spread but not definitive proof of greater virulence.
- The timing and magnitude of a possible second peak this season are uncertain; historical seasons have produced a second wave in some years, but it is not guaranteed.
- The precise degree to which recent federal guidance changes affected childhood vaccination rates in Massachusetts this season is not fully quantified and requires further evaluation.
Bottom line
Massachusetts is experiencing an early and intense influenza surge driven by widespread circulation of H3N2 subclade K, declining vaccine coverage, and holiday-associated transmission. Surveillance metrics — outpatient ILI share, rising hospitalizations, and daily ED burden — all point to a season that could last into spring and in some metrics match or exceed last year’s peak hospital impact.
Public-health and clinical priorities remain the same: increase vaccination uptake where possible, use masks in high-risk settings, stay home when ill, and seek medical attention promptly for at-risk individuals. Antiviral treatments are available and most effective when begun early; health systems are urging quick evaluation for vulnerable patients to reduce severe outcomes.
Sources
- The Boston Globe (local news; original reporting)
- Massachusetts Department of Public Health (state surveillance reports)
- Centers for Disease Control and Prevention — FluView (federal surveillance and burden estimates)
- Brown University Health (institutional health directive)
- UMass Chan Medical School / UMass Memorial (academic/clinical reporting)