Delayed Vaccines Tied to Whooping Cough Risk

September 13, 2013

By Andrew M. Seaman

NEW YORK (Reuters Health) Sep 13 - Children who are not vaccinated on the schedule recommended by U.S. health officials are at an increased risk of whooping cough, a new study shows.

Kids who fell significantly behind on their diphtheria, tetanus and acellular pertussis (DTaP) shots were between 19 and 28 times more likely to be diagnosed with pertussis than children who were vaccinated on time, researchers reported September 9th in JAMA Pediatrics.

Studies have shown pertussis cases have been on the rise across the U.S.

Researchers suspect that's due to the use of a new type of pertussis vaccine - which has fewer side effects, but is less effective over the long run - and to more children missing or delaying vaccination (see Reuters Health story of May 20, 2013).

Jason Glanz, the study's lead author from the Kaiser Permanente Colorado Institute for Health Research in Denver, and his colleagues compared the vaccination records of 72 children who were diagnosed with pertussis in one of eight healthcare systems between 2004 and 2010 and 288 similar kids who didn't get the disease. All were between the ages of three and 36 months.

The Centers for Disease Control and Prevention recommends children receive doses of the DTaP vaccine at two, four and six months of age, another dose between 15 and 18 months and a booster when they're four to six years old.

The researchers found that about 47% of children diagnosed with pertussis were not vaccinated according to that recommended schedule, versus about 22% of kids in the comparison group.

"Just over a third of the cases could have been prevented had they been vaccinated on time," Glanz told Reuters Health.

His team also found that the longer vaccinations were delayed, the higher the kids' risk of pertussis.

Those who were three doses behind, for example, were 19 times more likely to get whooping cough than kids who were caught up on their shots, and those who were four doses behind had 28 times the risk.

"I think the nice thing about this study is that it quantifies the risk," said Dr. Mary Healy, director of vaccinology and maternal immunization for the Center for Vaccine Awareness and Research at Texas Children's Hospital in Houston.

"Pertussis is a particularly serious disease. The difficulty with pertussis is that it's very often underappreciated how serious it can be," said Dr. Healy, who was not involved with the study.

In an ongoing pertussis outbreak in Texas, about 2,000 cases have been reported in the state this year. So far, two infants, who were too young to receive the DTaP vaccine, have died (see Reuters story of September 5, 2013).

Glanz said parents should understand that delaying their kids' vaccines puts the children at a greater risk of catching pertussis.

"The purpose isn't to demonize parents or marginalize them. We're doing this not because we're pro-vaccine but because we're pro-child," he said.

SOURCE: http://bit.ly/14Pft6k

JAMA Pediatrics 2013.

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