The Minnesota Department of Health says they haven't seen this many cases of whooping cough since World War II.
MPR reports the increase in pertussis, more than 4,300 cases across the state, is likely due to the most recent version of a vaccine introduced in 1991. The vaccine was intended to reduce side-effects, but it was recently discovered that the vaccine doesn't offer protection against the highly contagious disease for very long.
A booster vaccine available for people 10 years old and older, but it is not required under Minnesota's school immunization law.
Other places in the country are also seeing an outbreak. In Vermont, health officials are calling the spike in whooping cough an epidemic and are advising everyone over the age of 19 to get a special booster shot.
The federal Advisory Group on Immunization Practices is reviewing the vaccine schedule and urged pregnant women to get the booster during every pregnancy.
Pertussis is most severe for babies. More than half of infants younger than one years old who get the disease are hospitalized.