State health officials are trying to find out why so many children came down with the chickenpox in the Gale-Ettrick-Trempealeau School District in southern Trempealeau County---despite vaccinations.
Forty-four students have gotten chickenpox. All but two had received vaccinations, which health officials say are 85% to 97% effective.
Wisconsin Immunization Program director Dan Hopfensperger says it's the state's largest outbreak he can recall among vaccinated children.
The only other similar case occurred at a Dane County school in 2003, where slightly fewer students were affected. Hopfensperger says the state never determined a cause in that outbreak
In 2001, Wisconsin began requiring all kindergarteners be immunized for chickenpox. The state had 487 cases last year -- down from more than five-thousand in 1996.