Early childhood immunizations promotes asthma
15 April 2009
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 TH2-type immune response or decreasing
microbial pressure, which shifts the balance between TH1 and TH2 immunity,"
writes 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
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
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