HealthDay News — Vaccines that contain acellular pertussis (DTaP) may not protect against pertussis infection as well as those that contain whole cell pertussis (DTwP), researchers think.

Among children born in 1998, those who received DTaP had higher rates of pertussis at follow-up compared with those who received DTwP for the first three doses in the primary series, Sarah Sheridan, BMed, of Queensland Children’s Medical Research Institute in Brisbane, Australia, and colleagues wrote in a research letter published in the Journal of the American Medical Association.

During the 1990s, DTaP (diphtheria, tetanus, and acellular pertussis) replaced DTwP (diphtheria, tetanus, and whole-cell pertussis) in many developed countries, including Australia and the United States, because it was associated with a lower risk for adverse events, including injection-site reactions and fever.

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However, recent increases in pertussis rates in both countries have raised questions about whether the switch from one vaccine to the other could be responsible. To further explore the issue, Sheridan and colleagues examined data on pertussis cases reported to the health department in Queensland from 1999 to 2008, which is considered the pre-epidemic period for the ongoing pertussis outbreak, and from 2009 to 2011.

DTaP replaced DTwP in publicly funded immunization programs beginning in March 1999; therefore, children born in 1998 received primary courses with DTaP only, DTwP only or a combination of the two vaccines.

Pertussis reporting rates were compared with primary course vaccination for 58,233 children in the 1998 birth cohort, of whom 69.5% received at least three doses of any pertussis-containing vaccine during the first year. A total of 267 first pertussis cases were reported among this cohort through 2011.

The researchers found that, children who received a three-dose DTaP had higher rates of pertussis compared with those who received a three-dose DTwP primary course in both the pre-epidemic period (13.2 versus 5.2 per 100,000 per year) and the outbreak period (373.1 versus 113.3 per 100,000 per year).

For those who received a mixed dose, rates in the current epidemic were highest for children who received DTaP as their first dose (409.0 versus 113.3 per 100,000 per year).

Higher rates of disease observed among children who received the acellular vaccine could be related to changes in the circulating Bordetella pertussis strains or differences in the immune responses induced by the two types of vaccine, the researchers suggested.

“The lesser protection provided by DTaP, both as the initial vaccine or full primary course, may be due to linked epitope suppression, when the initial exposure locks in the immune response to certain epitopes and inhibits response to other linked epitopes on subsequent exposures,” the researchers wrote.

“The challenge for future pertussis vaccine development is to address the benefit-risk trade-off highlighted by our study, and to develop vaccines that induce long-lasting protection from the first dose, without the adverse events associated with DTwP use.”

Two authors disclosed financial ties to GlaxoSmithKline and sanofi-pasteur, both of which manufacture pertussis-containing vaccines.

Sheridan S et al. JAMA 2012; 308: 454-456.