One hundred eighty-nine new cases of pertussis were confirmed in Minnesota in the past week. More than 3,500 cases of the bacterial infection have been reported so far this year, the Minnesota Department of Health said.
Pertussis, also known as whooping cough, causes a persistent, severe cough that sometimes lasts for months.
Three-quarters of Minnesota's cases have occurred in vaccinated people, said Kris Ehresmann, director of the infectious disease division at the Health Department.
"Definitely this outbreak has been driven I think, in fairness, more by waning immunity than by those folks who have chosen not to vaccinate," Ehresmann said.
A reformulated pertussis vaccine was added to the U.S. vaccine schedule in the late 1990s. The new vaccine doesn't appear to last as long as the original vaccine, which had more side effects. Ehresmann said.
She said there is much discussion within the public health community about what to do to control the pertussis outbreak in the U.S.
"It is clearly the highest number of cases that we've had in the post-vaccine era for sure," Ehresmann said. "It's definitely a situation that's happening in Minnesota and nationally, and it's gotten everyone's attention."