The outbreak of the bug, which causes projectile vomiting and diarrhoea, started in the beginning of the week and quickly spread. It is not known precisely how many children and teachers at Tungelsta School in Haninge, southern Stockholm have been infected.
"This is exceptional. I have never seen anything like it," head teacher Johan Ahlqvist told newspaper Dagens Nyheter. He added that, on Wednesday, 10 pupils had vomited during school hours and 20 percent of staff have been off sick since Monday.
Tungelsta School's website reported on Thursday that it would remain open as normal during the day, which led to criticism from parents. One father told tabloid Aftonbladet that he believed 160 of the school's 750 children have been infected by the winter vomiting bug. One mother said: "My daughter came home in panic because children vomited in school."
February is usually the worst month for outbreaks of the flu and the winter vomiting bug.