Dr. Anne Schuchat, director of the Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, told reporters that nationwide nearly 18,000 cases of whooping cough, or pertussis, have been reported since 2012, with nine deaths reported.
More than 2,500 cases were reported this year in Washington state, where health officials have declared a whooping cough epidemic, but other states have had outbreaks as well.
In Washington, high rates of pertussis occurred in babies age 1 and younger and in 10-year-olds.
Washington state has a very high rate of parents not vaccinating their children, but Schuchat said many of the 10-year-olds had been vaccinated, which might indicate the new vaccine may not last as long as the earlier vaccines, WebMD reported.
The CDC is investigating whether the switch from whole-cell to acellular pertussis vaccine in 1997 -- a vaccine with fewer complications -- might have contributed to the increase illness especially among young teens who had been vaccinated as children, Schuchat said.
U.S. children are given the DTaP vaccine -- diphtheria, tetanus and pertussis -- in five doses.
Preteens ages 11 or 12 years should get a booster vaccine, called Tdap, the CDC recommends.
Reported cases of pertussis vary from year to year and tend to peak every 3-5 years. In 2010, 27,550 U.S. cases of pertussis were reported.