BOSTON — Boston is seeing a early surge in flu cases this year, city and health officials warned, with sharp upticks in cases and hospitalizations and even higher increases for children and teens as winter sets in.

“Flu cases are on the rise in Boston, and we are urging residents to protect themselves and their loved ones from respiratory illnesses which can cause hospitalization and severe illness,” said Public Health Commissioner Bisola Ojikutu. “Flu spreads easily during this time of the year when we gather together indoors. It is not too late to get vaccinated. Vaccination is the best tool we have to prevent serious illness.”

Boston’s flu cases surged 114% between the first two weeks of December, the City of Boston and Public Health Commission reported Tuesday. Flu-related emergency department visits also picked up 44% over the same time period.

The most recent week of cases saw nearly 700 confirmed cases reported on the city’s flu dashboard, almost seven times the number reported in the third week of December last year, marking an early rise in infections this flu season.

Last year’s flu season peaked at about 1,100 reported cases in early February 2025, according to the flu dashboard, and the year prior just nearly 340 in mid-February 2024.

Over the early December 2025 time-period, children saw the most rapid rate of infection increase, skyrocketing 217% for those age 5 to 17. Kids under 5 years old saw an increase of 83%, BPHC data reported.

This year’s spike comes as global health officials are monitoring a new “subclade K” strain of the influenza virus spreading across the countries including the U.S. The World Health Organization states that current data does not indicate increased severity with the variant, but it reflects a continued evolution of the virus.

Boston health officials said residents, especially children and older adults at high risk, are encouraged to get an annual flu vaccine. As of Dec. 6, only 30% of Boston residents were vaccinated for the flu, BPHC reported.

“Vaccines are highly effective at lowering the risk of severe illness and hospitalization from the flu and are essential for keeping yourself and your community safe this winter,” a BPHC release stated.

BPHC also encouraged residents to practice prevention strategies like hand washing, increasing ventilation and staying isolated when sick. Residents in households with members at high risk of severe disease “should consider wearing a mask” for added protection from respiratory illnesses.

People under two or over 65 years old, immunocompromised, pregnant, and with chronic illness may be at high risk, BPHC said, and should seek medical care when exposed or experiencing symptoms as early treatment can prevent serious illness.

City wastewater data, reported on a dashboard, also showed a 909% increase in COVID-19 over the last two-week trend reported in early December, though levels remain relatively low historically in Boston.

The department has hosted 27 free vaccine clinics in 15 neighborhoods this year, BPHC said, vaccinating over 2,500 people.

The city’s free vaccine clinics will continue for anyone over 6 months old across Boston in January. More information on the sites can be found at boston.gov/vaccine-clinics or the Mayor’s Health Line at 617-534-5050.

Vaccine appointments for flu and COVID-19 can also be made at local pharmacies, community health center, primary care physicians, and more. Vaccine locations can be found through vaccinefinder.org.

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