Doctors may need to reconsider the current schedule of whooping cough vaccinations in order to prevent outbreaks, researchers say.
In a recent study of the 2010 whooping cough outbreak in California, researchers found that kids between ages 8 and 12 were vulnerable to whooping cough even though they had been vaccinated against the highly contagious bacterial infection, which is also known as pertussis. These children had a higher rate of whooping cough than vaccinated children of other ages, the researchers said.
The finding suggests children may need to receive whooping cough booster shots earlier than they do currently, perhaps as young as age 8, to prevent immunity from waning to the point where children become susceptible to the disease, said study researcher Dr. David Witt, an infectious-disease physician at Kaiser Permanente Medical Center in San Rafael, Calif.
Currently, children receive their last dose of the five-shot vaccine series between ages 4 and 6, and then get a booster shot at age 11 or 12.
The vaccine's protection "doesn’t seem to last as long as the five to seven years that would be required" to keep children from getting sick in the years between the end of the series and the booster, Witt said.
Experts say more research is needed to confirm the findings, and it's unlikely the current vaccination schedule will be changed anytime soon.
The first version of the whooping cough vaccine, known as the whole cell pertussis vaccine, provided long-lasting immunity, but there were concerns about the vaccine's safety.
In 1997, a more purified version of the vaccine, with fewer side effects, was introduced. However, recent research suggests that the immunity this newer version provides is not as durable.
In 2010 California experienced its largest outbreak in 53 years, with 10,000 pertussis cases and 10 deaths.
In the new study, researchers examined medical records from 132 children who were treated for pertussis during the outbreak at the medical center where Witt works. They also looked at vaccination rates among children at the center who didn't develop the disease.
The rate of whopping cough among vaccinated children was about 245 per 10,000 for children ages 8 to 12, compared with 36 per 10,000 for children ages 2 to 7. (The rate for unvaccinated children was higher, at about 320 per 10,000 children ages 8 to 12.)
The researchers determined the vaccine was 41 percent effective in protecting children ages 2 to 7, but only 24 percent effective in protecting children ages 8 to 12. It was 79 percent effective in protecting those ages 13 to 18.
A whooping cough booster shot at age 8 would "lessen the burden of pertussis disease," said Dr. Paul Offit, director of the Vaccine Education Center at the Children's Hospital of Philadelphia, but "it would be a burdensome thing to do."
A booster scheduled for this age would require a doctor's visit at a time when kids don't typically have one, Offit said. Children usually go to the doctor for shots in their younger years, and then again at ages 11 or 12, when entering middle school. "There's not really a platform on which to build that vaccine," Offit said.
Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University School of Medicine, said the first line of action will be to make sure everyone currently recommended to receive a whooping cough vaccine gets it, including adolescents ages 11 to 12 and adults. This will lessen the amount of circulating pertussis disease and lower the chances that those with waning immunity will become infected, Schaffner said.
After the current vaccine schedule is properly implemented, researchers could take another look at whether to recommend a booster shot around age 8, Schaffner said.
The study is published in the June issue of the journal Clinical Infectious Diseases. It first appeared online March 15.