There's been a huge uptick in cases of pertussis, better known as whooping cough, in Wisconsin.
The Centers for Disease Control reports this year there have been nearly 5,700 confirmed and probable cases in the state alone this year.
In comparison, there were only about 1,200 at this time last year.
Wisconsin has the nation's highest rate of whooping cough cases, averaging about one for every 10,000 people.
Pertussis is a highly contagious illness that for adults tends to be an annoying cough, but it's potentially deadly for infants.
Doctors say the reason for the spike in cases is the redesigned vaccine introduced about 20 years ago in order to reduce the side effects.
"There's a problem, and the problem being is it doesn't have a big enough punch," says Dr. C.J. Menagh, with Mayo Clinic Health System in La Crosse, "it's very good that it doesn't make people sick anymore and doesn't give you sore legs and that kind of thing, but we would like it to be a better vaccine."
On average, Mayo Clinic Health System is seeing between 10 and 15 cases; Gundersen Lutheran says its number is closer to 25.
Health experts say it can be tough for a patient to realize they have whooping cough, especially during cold and flu season. However, some early symptoms can help a person differentiate between the three.
"Typically with pertussis it's going to start with your upper respiratory symptoms, you'll have a runny nose or a sore throat, runny eyes, it will present like an upper respiratory viral infection," says Marilyn Michels, with Gundersen Lutheran.
The pertussis vaccine is supposed to last for about 10 years... but is only about 85% effective and it wanes over time.
Michels says one person from Wisconsin has died from whooping cough this year.