A man gets vaccinated against flu and Covid-19 in Boston, one of many places seeing a surge in flu cases. (Photo Credit: Suzanne Kreiter/The Boston Globe/Getty Images via CNN Newsource)

(CNN) — After a record week of flu activity in the US, hospitalizations and deaths continue to rise.

About 40,000 people were admitted to the hospital with flu during the week ending January 3, according to data published Friday by the US Centers for Disease Control and Prevention, âabout 10% more than the â36,600 hospitalizations in the week before. Overall, there were about 12 flu hospitalizations for every 100,000 people in the US last week, CDC data shows.

Seniors are most likely to be hospitalized with flu, but rates among children are also high. At least 17 children have died from the flu this season, the CDC says – a number that nearly doubled over the past week, with eight new deaths reported.

Four of the pediatric flu deaths this season have been in Massachusetts, including two children in Boston who were under the age of 2.

“Flu cases are surging in Boston, and we are seeing an uptick in serious cases involving children, including the tragic deaths of two very young children,” Dr. Bisola Ojikutu, the city’s commissioner of public health, said in a statement.

“While the flu is usually mild, it can cause hospitalization and death. Children under the age of two are at higher risk. Parents should get their children ages six months and older vaccinated as soon as possible to decrease the risk of severe complications. Parents should seek immediate medical attention if their child has flu symptoms and also has signs of more severe illness, like trouble breathing, decreased urination, persistently high fever or becomes extremely lethargic and difficult to arouse.”

Overall, the CDC estimates that there have been at least 15 million illnesses, 180,000 hospitalizations and 7,400 deaths from flu this season.

Flu activity “remains elevated across the country,” and the CDC says it expects that to continue for several more weeks. More than a dozen states have flu activity levels in the highest category that the agency tracks.

CDC surveillance data published last week showed that flu-like activity in the US had reached the highest level on record since the agency started tracking about 30 years ago.

This week, some of those indicators have fallen, but the CDC says that does not necessarily mean the season has reached its peak. Instead, the downtick “could be due to changes in healthcare seeking or reporting during the holidays,” and more increases may come in the weeks ahead.

Influenza A(H3N2) viruses are the most commonly reported, and additional genetic testing suggests that a new variant — called subclade K — that caused early and busy flu seasons in other part of the world continues to be driving the vast majority of cases in the US.

Vaccination “has been shown to reduce the risk of flu and its potentially serious complications,” the CDC says. But only about 130 million doses of vaccine have been distributed nationwide this season, enough to cover less than 40% of the US population.

Earlier this week, the US Department of Health and Human Services overhauled the childhood vaccine schedule, including an updated recommendation that decisions on vaccinations against flu be based on “shared clinical decision-making,” which means people who want one must consult with a health care provider.

Many state health departments have broken with these updated recommendations, instead supporting recommendations from professional medical associations — such as the American Academy of Pediatrics — that continue to broadly support flu vaccination for everyone 6 months and older.

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