Destefano F, Gu D, Kramarz P, et al. Pediatr Infect Dis. 2002;21:498–504
Purpose of the Study.
A few previous studies have suggested that childhood vaccines may increase the risk of asthma, especially whole cell pertussis vaccine. The aim of this study was to evaluate the suggested association between childhood vaccination and risk of asthma.
A cohort of 167 240 children enrolled in 4 large health maintenance organizations in the western United States was followed from birth until at least 18 months to a maximum of 6 years.
Vaccination status of patients was obtained from data collected by the Vaccine Safety Datalink created by the National Immunization Program of the Centers for Disease Control and Prevention (CDC). Asthma cases, defined by criteria discussed in the article, were identified using computerized medical encounter forms and pharmacy databases. To differentiate between asthma and bronchiolitis, a child had to have at least 1 asthma diagnosis or medication after age one. Proportional hazards regression analyses were conducted to estimate relative risks of developing asthma according to vaccination status.
A total of 18 407 children (11%) developed asthma, with a median age at onset of 11 months. The relative risks of asthma were the following: 0.92 for diphtheria, tetanus, and pertussis (DTP) vaccine; 1.09 for oral poliovirus vaccine (OPV); 0.97 for measles-mumps-rubella (MMR) vaccine; 1.18 for Haemophilus influenzae type b (Hib) vaccine; and 1.20 for hepatitis B vaccine (HBV). The Hib result was not consistent across health maintenance organizations. In a subanalysis restricted to children who had at least 2 medical encounters during their first year of life, the relative risks decreased to 1.07 for Hib and 1.09 for HBV.
There is no association between the DTP, OPV, or MMR vaccines and the risk of asthma. The weak associations for Hib and hepatitis B vaccines seem to be at least partially accounted for by health care utilization or information bias.
Concerns regarding vaccine side effects and relative risks of illnesses from vaccinations are an important issue for parents, as demonstrated by the long debate about MMR and autism. As always, it is important to regard these results within the context of the article. Although the study found a small increased risk of asthma with Hib and hepatitis B vaccines, the authors state that there were potential limitations of their study including confounding factors, possible misclassification of asthma status, and relative short follow-up that may have led to an overestimate of these risks.