An outbreak of the flu forced school officials to canceled classes at all three Fairplay, Colo., schools Thursday.

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Officials said about 30 percent of the student body in the three Park County schools was absent Wednesday. A Silverheels Middle School, the absentee rate was 40 percent.

The schools will be closed Thursday to allow workers four days to disinfect the buildings. Fairplay schools are on a Monday through Thursday schedule.

All three schools are adjacent to one another in Fairplay.

Statewide, there are 1,525 confirmed cases of influenza. Last year, Colorado had 2,681 flu cases, including 19 fatalities. Another 748 died from flu-related complications.

The strain of flu showing up this year is part of a deadly group called H3N2, a type of flu that leads to more deaths and hospitalizations than other flu strains, health officials said.

But because this year's flu vaccine targets a slightly different type of H3N2 flu than patients are getting, doctors have no idea how well the vaccine will work. The virus changes slightly over time, a change doctors call "drift," which is why doctors suggest getting a new flu shot every year.

The shot is recommended for adults over 50, children between 6 months and 2 years, people with chronic medical conditions and people who work in health care

To get more information on the flu and its symptoms, you can call the Colorado flu hotline from 7 a.m. to 11 p.m. at (877) 462-2911. To find out where there's a flu shot clinic near you, call (888) 692-0269.