(NBC News) Flu outbreaks are popping up across the country.
For the second day in a row Wednesday classes were canceled at Nazareth Academy near Chicago, where an outbreak of the flu has hit a quarter of the student body.
Schools in Kansas City and Dallas have also been hit hard.
Flu is now widespread in six states: Alaska, Florida, Illinois, Louisiana, Maryland and North Carolina, and cases are peaking earlier and earlier in the typical flu season.
“For the last couple of seasons, they’ve actually been peaking around the winter holiday times, and so we think that’s what might happen again this year,” says Dr. Dan Jernigan of the Centers for Disease Control.
About half of the flu viruses circulating have mutated into forms not covered in this season’s vaccine, making it less effective. Still, experts urge vaccination.