Study links delayed vaccines to increased risk of whooping cough

The Texas whooping cough outbreak has increased awareness of suspected limitations of the current vaccine and the risks of refusing to get immunized. Yet outright refusal of all vaccines is relatively rare, with more parents choosing to delay or omit certain shots in the belief that this is the safest approach.

Research published in JAMA Pediatrics reveals flaws in this reasoning. While there is no evidence to suggest alternative immunization schedules cut the risk of adverse events, the JAMA paper shows they do increase the likelihood of contracting disease. In the paper, Kaiser Permanente researchers show that kids who fall significantly behind on diphtheria, tetanus and acellular pertussis (DTaP) shots are 19 to 28 times more likely to catch whooping cough.

"Just over a third of the cases could have been prevented had they been vaccinated on time," lead study author Jason Glanz told Reuters. The link between delayed vaccinations and increased risk of disease is unsurprising, but the study delivers data to back the widely held suspicions. Quantifying the risk of delaying whooping cough shots could help healthcare providers win over skeptical parents.

In recent years, some parents have opted for alternative immunization schedules--such as one published by Dr. Robert Sears--in an attempt to offset perceived risks of vaccinations.  Sears' pertussis schedule closely mirrors Center for Disease Control and Prevention (CDC) recommendations, but other vacciness are delayed by months. The first dose of polio vaccine, for example, is given when an infant is 9 months old, 7 months later than CDC recommends. 

Polio is one of the few diseases for which immunization levels are above CDC targets. Data published this week shows 92.8% of infants are fully vaccinated against polio. In contrast, 82.5% of infants have received all four doses of DTaP, the combination vaccine that protects against whooping cough. After gathering data showing the risks of under-vaccinating, the Kaiser Permanente researchers are keen to communicate the message to worried parents. "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," Glanz said.

- read the Reuters article
- check out the JAMA abstract
- here's the CDC data (PDF)