The number of serious influenza cases in Minnesota dropped again last week, returning to normal annual levels after an unusually harsh start to the flu season in December.

The number of flu patients requiring hospitalization dropped sharply for the second time, to 21, after climbing above 300 per week in late 2014. The number of school outbreaks, which rose in December to the highest level in at least five years, also returned to typical levels. No new deaths were reported.

Outbreaks in long-term care facilities dropped for the second time in four weeks but remained higher than normal — a particular concern because the circulating H3N2 strain of influenza also has historically been associated with more severe illnesses in young children.

Flu season typically wanes by January or February, but public health officials continue to urge people to get vaccinated. Although this year's vaccine is poorly matched to the current mix of flu strains, with an estimated effectiveness of 23 percent, it can still offer individuals some protection and limit circulation of the virus, officials say.