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CME Released: 4/14/2008
Valid for credit through: 4/14/2009
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April 14, 2008 — Childhood asthma is reduced by half when the first dose of diphtheria, pertussis, and tetanus (DPT) is delayed by more than 2 months vs given during the recommended period, according to the results of a retrospective longitudinal study reported in the March issue of the Journal of Allergy & Clinical Immunology.
"Early childhood immunizations have been viewed as promoters of asthma development by stimulating a T H 2-type immune response or decreasing microbial pressure, which shifts the balance between T H 1 and T H 2 immunity," write Kara L. McDonald, MSc, from the University of Manitoba in Winnipeg, Manitoba, Canada, and colleagues. "Differing time schedules for childhood immunizations may explain the discrepant findings of an association with asthma reported in observational studies. This research was undertaken to determine whether timing of diphtheria, pertussis, tetanus (DPT) immunization has an effect on the development of childhood asthma by age 7 years."
The investigators analyzed data from the complete immunization and healthcare records of a cohort of children born in Manitoba in 1995, from birth until age 7 years. Using multivariable logistic regression, they computed the adjusted odds ratio for asthma at age 7 years according to the timing of DPT immunization.
Among 11,531 children who received at least 4 doses of DPT, the risk for asthma was halved in children in whom administration of the first dose of DPT was delayed by more than 2 months. For children with delays in administration of all 3 doses, the likelihood of asthma was 0.39 (95% confidence interval [CI], 0.18 - 0.86).
"We found a negative association between delay in administration of the first dose of whole-cell DPT immunization in childhood and the development of asthma; the association was greater with delays in all of the first 3 doses," the study authors write. "The mechanism for this phenomenon requires further research."
Limitations of this study include possible ascertainment bias; findings not yet confirmed with the diphtheria, acellular pertussis, tetanus (DaPT) vaccine; and inability to refute the issue of early-life infections as an explanation for the association between delayed immunization and protection against the development of asthma.
"Further study is vital to gain a detailed understanding of the relationship between vaccination and allergic disease, because a perception that vaccination is harmful may have an adverse effect on the effectiveness of immunization programs," the study authors conclude.
The Canadian Institutes of Health Research supported this study. Some of the authors have disclosed various financial relationships with the Western Regional Training Center for Health Services Research, the National Training Program in Allergy and Asthma, the Canadian Institutes of Health Research, Allergen, and/or Novartis.
J Allergy Clin Immunol. 2008;121:626-631.
Early childhood vaccinations may promote development of asthma, directly by stimulating a T H 2-type immune response or indirectly by decreasing microbial pressure. In support of this hypothesis, an IgE response to vaccine antigens often occurs in children vaccinated with diphtheria/tetanus, and this response is more pronounced among individuals with atopy.
Epidemiologic evidence linking DPT immunizations to childhood asthma is inconsistent. Some studies show an increased or decreased risk of developing asthma, whereas others show no association. This study assessed whether timing of DPT vaccination affects the risk of developing childhood asthma by age 7 years.