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.
The Role of 'Vaccine Refusers'
Another possible reason whooping cough rates are rising: "vaccine refusers." These are parents who choose not to get their kids vaccinated because they believe vaccines may not be safe.
"It's hard to say how big a contributing factor this is,” says Romina Libster, MD, an expert in infant immunization. In a recent outbreak in California, she says that most of the children who got whooping cough were immunized.
But more parents are choosing to delay or refuse the recommended childhood vaccines, Libster says. And when there isn't a very high vaccination rate, the population as a whole becomes less immune to a disease.
People who are opposed to vaccines may be creating a pocket where the disease can take hold. "This allows the disease to explode," Tan says.
Some Vaccinated People May Still Spread Whooping Cough
Another possible cause of the spike in whooping cough cases: People who get the newer vaccine are protected against the disease, but they may still carry the bacteria and spread it to those who aren't vaccinated.
That kind of situation was reported in a study of baboons that was published in 2013. Researchers vaccinated some animals with the new vaccine and some animals with the old vaccine. Animals in both groups were protected against whooping cough. But the animals that had the newer version had whooping cough bacteria in their airways for as long as 6 weeks. Those with the older version only had the bacteria in their airways for 3 weeks.
Some health experts think a new version of the vaccine is needed to bring down the number of people getting whooping cough. "We need a better vaccine that induces lifetime, or at least longer, immunity," says Roy Curtiss, PhD, director of the Center for Infectious Diseases and Vaccinology at Arizona State University. That may mean trying a combination of older and newer vaccines, more frequent booster shots, or something completely new.
In the meantime, the best way to protect yourself and your kids from whooping cough is to follow the CDC's recommended vaccine schedule. The vaccine that protects against whooping cough for kids younger than age 7 is called DTaP. It also prevents diphtheria and tetanus. Make sure your child gets all the scheduled doses.
For older children and adults, the vaccine that protects against whooping cough is called Tdap. Like DTaP, it's a combination vaccine that also prevents diphtheria and tetanus. A booster for Tdap is recommended for all adults. And pregnant women should get a Tdap booster in the third trimester.