Record number of cases expected this year.
Whooping Cough was once nearly eliminated in the United States.
Now it is coming back with a vengeance.
So far this year there have been more than 18,000 cases reported to the Centers for Disease Control and Prevention, and nine babies have died.
People in Washington State are flooding health clinics and rolling up their sleeves to get a Whooping Cough booster shot.
There have been more than 3,000 cases of the illness reported in that state alone, more than triple the amount from last year.
"It's really important for teenagers and all adults to get the booster shot," advises Mary Selecky, Secretary of Washington State's Department of Health.
Other states are seeing higher than normal activity as well according to the Centers for Disease Control.
"It's of epidemic proportions," says the CDC's Dr. Tom Clark. "This is the largest number of cases we've seen since the 1950s."
Many of the cases are in 10-year-olds who got the Whooping Cough vaccine as children but haven't yet received the booster shot recommended at age 11.
"Kids who are 10 years of age, about three in ten kids, are still susceptible, despite having been vaccinated. So really, the majority of the cases are occurring in vaccinated but susceptible kids," Dr. Clark explains.
Experts are also seeing a high number of cases in young teens who got the booster.
They say the shot still works, but maybe not as well as they thought.
"It looks now like the protection is wearing off, but we're not sure to what degree, so that's the focus of our investigations," Clark says.
It's those who are too young to be vaccinated who are the most vulnerable.
More than half of infants with the illness need to be hospitalized.
The CDC recommends all caretakers, especially mothers, get a Whooping Cough booster shot.
Children with Whooping Cough have an uncontrollable, violent cough that makes it hard to breathe.
Patients often need to take deep breaths that are marked by a whooping sound.
They may also have a slight fever and flu-like symptoms.
Parents who notice these symptoms should have their child checked out right away.