Journal of Pediatrics
May 2013, Vol. 162, No. 5
http://www.jpeds.com/

Protection wanes 5 years after the 5th dose of DTaP
Jennie S. Lavine, PhD
http://www.jpeds.com/article/S0022-3476%2813%2900254-0/fulltext

Question
Among children immunized with 5 doses of diphtheria, tetanus, and acellular pertussis vaccine (DTaP), what is the association of development of pertussis with time elapsed from the last dose?

Design
Case-control study comparing the time from the 5th dose of DTaP in children testing positive for pertussis, with both those testing negative for pertussis, and matched healthy controls.

Setting
49 medical clinics and 19 hospitals in Northern California.

Participants
Children, 4-12 years old, who are members of Kaiser Permanente of Northern California.

Intervention
Secondary analysis of the Kaiser Permanente Database.

Outcomes
The primary outcome was comparison of patients who were polymerase chain reaction (PCR)-positive with patients who were PCR-negative controls. The secondary outcome was comparison of patients who were PCR-positive with matched healthy controls.

Main Results
277 children, 4 to 12 years of age, who were PCR-positive for pertussis were compared with 3318 PCR-negative controls and 6086 matched controls. Children who were PCR-positive were more likely to have received the 5th DTaP dose earlier than PCR-negative controls (P < .001) or matched controls (P = .005). Comparison with PCR-negative controls yielded an OR of 1.42 (95% CI: 1.21-1.66), indicating that after the 5th dose of DTaP, the odds of acquiring pertussis increased by an average of 42% per year.

Conclusions
Protection against pertussis waned during the 5 years after the fifth dose of DTaP.

Commentary
Resurgence of pertussis has spurred many studies on the effectiveness of current vaccines.1 The switch from whole-cell to acellular vaccine (DTaP) in the 1990s may be partly to blame for the increased incidence. Klein et al demonstrate that immunity induced by DTaP wanes quickly (controlling for vaccination history and case diagnosis). Their study includes patients who should have received only DTaP and cases diagnosed by standardized PCR. Additionally, Klein et al address doctors’ varying propensity to test for pertussis by comparing the cases with children who were PCR-negative who experienced similar testing biases. The study does not include unvaccinated or whole-cell vaccinated controls, so factors other than DTaP’s efficacy may contribute. Nonetheless, this study is a wake-up call: DTaP’s short-lasting effectiveness means that protecting infants via herd immunity is impractical, even with booster doses. Future research is needed to ascertain the causes of the shortened duration of immunity and to develop a better vaccine.2, 3 In the mean time, strategies for protecting infants is the priority. Despite its short duration, DTaP’s primary efficacy is high. Given the results of the current study, “cocooning” infants (ie, administering booster doses to parents and older siblings) is both logical and necessary.