(Newsweek) Hundreds of students in two schools in the same Minnesota city were out sick throughout the past week due to symptoms of the flu or a “flu-like” illness.

The illness appeared to afflict mainly students attending West Middle School and Sun Path Elementary School, the Star Tribune reported. Both schools are part of the Shakopee School District in Shakopee, Minnesota, and are just two and a half miles apart.

According to a short news release on the school district’s website, more than 300 students at West Middle School called in sick Monday because of flu-related sickness and symptoms.

They represented more than a quarter of the entire number of students at the school, who the district said numbered 1,165.

Sun Path Elementary reported that 100 students out of the entire body of 593 students (around 17 percent) were absent last week because of the flu, according to the school district.

“As always, we encourage parents and guardians to keep their students home if they are exhibiting flu-related symptoms,” Superintendent Mike Redmond said in a statement on the school district’s website. “We are taking the necessary precautions, and will continue to monitor the situation and take appropriate action, as needed.”

This year’s flu season, which will last from October to May, has already shown signs of being out of the ordinary, according to Minnesota CBS affiliate WCCO-TV.

Kris Ehresmann, director of infectious diseases at the Minnesota Department of Health, told the channel that of the two strains of the influenza virus harmful to humans—influenza A and influenza B—the former usually affects the most people at this time of the year.

Influenza B typically does not appear in high numbers until late in the winter. However, in the current flu season, influenza B has afflicted most people with the flu. Ehresmann told WCCO-TV that young people are especially susceptible to influenza B, which might partly explain the high number of cases at West Middle School and Sun Path Elementary.

According to data from the Minnesota Department of Health, 55 outbreaks of the flu have occurred in the state’s schools since the beginning of the flu season in October. Thirteen of those outbreaks occurred in the first week of December.