Massachusetts is seeing a sharp spike in cases of influenza.

Since Feb. 1, flu severity in the state has been classified as “very high” by the Centers for Disease Control and Prevention. The latest state data shows higher rates of flu-like illness than any other winter peak in years — and cases are still trending upward. Clinicians at local hospitals say this season has been the harshest they’ve seen in some time.

“One of the remarkable things is that we’re seeing … more respiratory illness caused by influenza than caused by COVID-19,” said Dr. Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital. “That’s the first time that’s happened since the pandemic.”

Nearly 11.5% of patient visits in the last week were for flu-like symptoms, according to

data from the Massachusetts Department of Public Health.
That’s compared to 5% of visits for the same time period in 2024 and just 2% in 2023.

UMass Medical Center Infectious Disease Specialist Dr. Sandeep Jubbal said he thinks the weather could be one of the main causes of the spike.

“Flu is a virus with a short incubation period that lasts one to four days, which means that symptoms typically begin within two days after being exposed,” said Jubbal. “That’s why we’re seeing this steep upslope in cases when referring to the curve, and it basically coincides with the time where we all moved indoors due to the cold weather.”

Jubbal also said that while flu vaccination rates among those age 65 or older are fairly high, only about 45% of children across the U.S. have received the vaccine.

“This is a virus that spreads close, congregate settings, and based on children going to school, is a high risk factor,” he said. “That’s why vaccinating kids is also very important in decreasing the overall burden of infection and the number of cases.”

Hospitalizations for influenza are at nearly 9% in Massachusetts, the highest since December 2022.

Nationwide, dozens of other states are also experiencing high spread of the virus. The

CDC estimates
at least 29 million people have been sick with the flu so far this season and about 16,000 have died.

Sax said that while generally healthy individuals are unlikely to require hospitalization, the flu can be severe for certain populations.

“The people we worry about the most are people with current medical illnesses, people at the extremes of age and pregnant women,” he said. “We know that those groups have much higher rates of flu complications.”

Both Sax and Jubbal emphasized that there’s still time to get the influenza vaccine.

“Vaccination cannot guarantee that it’s going to prevent someone from having an infection, but definitely at least moderately, usually shorter sick days, and it does help in preventing the spread,” said Jubbal. “We can’t control the weather, but we can definitely control the vaccination.”

“It takes only a couple of weeks for the flu vaccine to start generating antibodies to protect you, and one thing these numbers are telling us is that it’s not not going away any time soon,” he said.

While Sax and Jubbal both agree that rates will continue to increase, Jubbal said he expects the curve to reach a plateau and ultimately downslope as the weather improves.