The US is facing its worst epidemic of whooping cough since the 1950s, according to the Centers for Disease Control and Prevention, which recommends that adults—especially pregnant women and those who spend time around children—get booster shots. Some 18,000 cases of the highly infectious disease have been reported to the CDC so far this year, more than twice as many as at the same time last year, reports NBC. Nine children have died, and infections are on course to hit levels not seen since 1959, when there were 40,000 cases.
"My biggest concern is for the babies. They're the ones who get hit the hardest," says the chief of the health department in Washington, one of the worst-affected states. Officials aren't sure what's behind the surge in cases, but they suspect that a new vaccine for children introduced in the late '90s is proving to be less effective long-term than the one it replaced. Adults are supposed to have at least one dose of whooping cough vaccine, but the CDC says only some 8% have complied.