The second week of December was a nasty one for seasonal influenza in Minnesota, with 203 schools reporting outbreaks of flu-like illness and 60 people hospitalized, according to figures released Thursday by the state Department of Health.

The state also confirmed a second flu-related death of someone younger than 18.

“We have seen an amazing surge in new outbreaks, especially in schools, as of last week,” Dr. Andrew Thompson, an infectious disease specialist at St. Luke’s hospital in Duluth, said Thursday. “It started in the southeast corner of the state a couple weeks ago, where we started to see the first high level of activity. It seems now like it has hit the whole state; there have been a number of cases in our community.”

Flu fears have been building since Thanksgiving, when health officials identified a circulating A strain of influenza that is known to cause more severe illnesses

and is poorly matched to this year’s vaccine. At least one Twin Cities-area school closed early for the holidays this week to prevent the further spread of illness in its halls and classrooms, and some hospitals in the state - including Fairview Range Medical Center in Hibbing - have imposed new rules to discourage or restrict visitors.

“We’ve seen more flu patients this year already than all of last year combined,” said Dr. John Wald, medical director for public affairs at Mayo Clinic in Rochester, which is providing specialized treatment to patients whose infections have resulted in severe breathing problems.

Duluth-based Essentia Health hasn’t imposed any special rules but is asking visitors to use common sense, spokeswoman Maureen Talarico said.

“We’re asking people to self-monitor,” she said. “If you feel that you’re coming down something it’s best to stay away and visit your loved one when you’re feeling better.”

Thompson said St. Luke’s is considering limiting visitors, but restrictions were not in place as of Thursday.

The number of school cases last week was a huge spike from the first week of December, when only 19 schools suffered outbreaks. Schools report outbreaks to the state Health Department when they are missing 5 percent or more of their students to flu-like symptoms, or when elementary schools have three more students absent from the same classroom.

It was the highest weekly number of school outbreaks since at least 2010.

At least some schools in the Northland, though, were not reporting any significant flu outbreaks on Thursday.

“Our school nurses are seeing some cases of influenza-like symptoms, but no unusual numbers or spikes,” said Duluth school district spokeswoman Katie Kaufman.

Proctor Superintendent John Engelking also said that his district had not seen any “abnormal spikes” that would require reporting to the state.

Outbreaks in long-term care facilities also increased in the latest report. There were 18 last week, compared to four the prior week. Flu infections in these facilities raise particularly concern because influenza is known to be harsher in the elderly and people with chronic illnesses.

Flu strain mutations Thompson said researchers from around the world worked together before the flu season to decide - through modeling and calculations - on the three or four most likely flu strains, and based a vaccine on that.

In the intervening months, the H3N2 strain had some genetic mutations that have lessened the effectiveness of the vaccine.

“I would say they didn’t miss the mark, but the mark changed early in the year,” he said.

But, Thompson noted, “that does not mean the vaccine is totally ineffective. … It might be pretty good; it might be not good at all. …

“Even in a year where it’s perfectly matched, the vaccine is not a perfect vaccine. In a good year with a perfect match we still see the flu, however it reduces the severity and duration and the risk you’ll end up in hospital by 50 percent.”

The state report issued Thursday said five people were hospitalized with cases of influenza in Northeastern Minnesota in the second week of December, bringing the season total to 10 in the region.

Statewide, 60 people were hospitalized with the flu in the second week of the month, compared with 22 in the same week last year. The median age of the people hospitalized was 66.

The identities of the children who died from influenza aren’t provided by the Health Department. Flu was suspected, but not publicly confirmed, in the death of an otherwise healthy 17-year-old from Owatonna, Minn., earlier this month.

News Tribune reporters Brady Slater, Tom Olsen and John Lundy contributed to this report.