MINNEAPOLIS (AP) — Flu season in Minnesota is off to an unusual start, with the B strain of influenza causing most of the lab-confirmed cases instead of the A strain, which typically emerges first.

The Minnesota Department of Health released data Thursday showing that the B strain made up about 80% of the positive flu specimens obtained in clinics and hospitals that were tested in the first week of December, the Star Tribune reported. In Minnesota’s past 10 flu seasons, the A strain appeared first and did most of the damage, and B strains barely registered until February.

“Typically, an A strain will peak and then you’ll have B in the background and then you might see a second small wave of B,” said Kris Ehresmann, director of infectious disease for the Health Department. “But we haven’t seen this.”

B strains have historically spread faster among children. In the first week of December, just two flu outbreaks were reported in long-term care facilities, such as nursing homes. However, 13 were reported in schools. Outbreaks are reported in schools when they are missing 5% of their students, or three elementary students from the same classroom, because of flu-like ailments.

So far, a quarter of the 176 flu-related hospitalizations in Minnesota have involved children, a number that would be closer to 10% during a normal flu season, Ehresmann said.

Seasons with more B cases are more likely to be milder, but infected people can expect the same symptoms, such as fever, fatigue, sore throat and body aches.

No pediatric flu deaths have been reported this flu season. Two were reported last flu season. Health officials monitor that figure closely because flu-related deaths are most common in the elderly and people with chronic diseases. Deaths among children can signal a more severe season.

Flu vaccines remain bountiful, particularly for the B/Victoria strain that is now spreading, as well as for some other strains, Ehresmann said.