When a new whooping cough vaccine was introduced in the late 1990s, there were hopes for a lower infection rate. But there's been a puzzling trend: a spike in new cases.
More than 48,000 Americans had whooping cough in 2012 -- a 50-year high. The disease, also known as pertussis, brings on fits of coughing that can last for weeks in adults and older kids. For babies, especially very young ones, the symptoms can be life-threatening.
What's behind the increase in whooping cough? Experts aren't sure, but they have some theories:
The newer pertussis vaccine does not protect against disease for as long as the previous version.
Parents who don't let their kids get vaccines may be creating more opportunities for whooping cough outbreaks.
Even vaccinated people may still be carriers and spread whooping cough without realizing it.
The Newer Vaccine Doesn't Last as Long
Before 1997, the whooping cough vaccine used in the U.S. was a type known as a "whole cell" vaccine. It used all parts of the bacteria that causes whooping cough, explains Litjen Tan, PhD, chief strategy officer of the Immunization Action Coalition.
The vaccine was effective, but it had side effects, including sore arms, crying, fussiness, anxiety, and occasional seizures.
The newer vaccine, known as an "acellular" vaccine, only contains parts of the whooping cough bacteria. It has fewer side effects than the old version, Tan says.
At first, "the data showed that acellular worked as well as whole cell," Tan says. "But as time went on, immunity just started waning in children who got the acellular vaccine."
In other words, the new vaccine doesn't seem to protect people as long as the old one. And as the protection of the vaccine wears off, the number of whooping cough cases may rise.