Children of parents who refuse to have their children vaccinated against whooping cough are 23 times more likely to develop the disease than children who get the shots, according to a new study. The U.S. Centers for Disease Control and Prevention says whooping cough now infects more 5,000 children a year.
Authors of the study, which was conducted at Kaiser Permante Colorado's Institute for Health Research in Denver, say the results show a continued need to "to further understand why parents refuse immunizations and to develop strategies for conveying the risks and benefits of immunizations to parents more effectively."
Whooping cough or pertussis -- the medical name for the disease, causes a respiratory infection with an uncontrolled cough with a characteristic whoop or yelp -- said Dr. Jason Glanz, the lead author of the study.
Parents may shun the vaccines over the fear of rare but serious side effects associated with the use of some vaccines in certain individuals.
Many parents who refuse whooping cough vaccine make the argument that their children don't need to be vaccinated because peers -- friends and classmates -- have been vaccinated so all children in the group would be protected by a phenomenon known as herd immunity.
But Glanz said his study suggests that the herd immunity theory doesn't hold for pertussis.
"One of the misperceptions among parents is that the pertussis vaccine doesn't work and that their children are at low risk for infection, and our study showed that both were not true," Glanz said.
Glanz and his colleagues based that estimate on a case control study that compared children whose parents had refused vaccination to children who received vaccinations. The findings were published in the June issue of Pediatrics.
The researchers determined that 11 percent of whooping cough cases in the overall population were linked to vaccine refusal.
Dr. Gregory Poland, director of Mayo Clinic Vaccine Research Group in Rochester, Minn., said this study's results were consistent with others.
"Parents need to know they place their children at a documented and real risk, as well as others, when they refuse vaccines based on inaccurate information," he said.
He added, "This study shows that there is plenty of pertussis out there and it is highly contagious."
The CDC said the incidence of pertussis has increased steadily each year since the 1980s and in 2007 the incidence was 3.6 cases per 100,000 population.
The World Health Organization reported more than 200,000 whooping cough deaths in 2000 world-wide.
Initially the symptoms mimic the common cold -- upper respiratory congestion and a cough. But the cough rapidly progressed to the characteristic whoop or yelp in rapids succession or paroxysms. In infants complications included pneumonia, seizures, brain swelling, and death. Adults are also at risk for pneumonia and rib fractures caused by coughing.
The rate of vaccine refusal in the United States remains low, typically measured by counting non-medical exemptions from required school immunizations. But it has increased over the past two decades.
This could be the result of parents' attention shifting from the dangers of vaccine-preventable illnesses to issues of vaccine safety as the diseases become rarer, Glanz and colleagues said.