Risk factors for invasive Haemophilus influenzae disease among children 2-16 years of age in the vaccine era, Switzerland 1991-1993

Background. Continued surveillance, and detailed investigation of direct and indirect effects of conjugated vaccines and risk factors for invasive H.influenzae serotype b (Hib) disease in the vaccine era are important. Methods. 143 cases with invasive disease between 1991 and 1993 aged 2-16 years were selected retrospectively from a large incidence trend study, Controls (n = 336) were recruited from local vital registries and matched to cases for age, gender, and residence. Hib vaccination histories among study subjects and their siblings and other sociodemographic variables were obtained by questionnaires completed by the parents of these children. Adjusted odds ratio (OR) estimates were calculated by conditional logistic regression analysis. Results. Most vaccinated subjects had received the Polysaccharide-Diphtheria Toroid vaccine and estimated vaccine efficacy was high (95%; 95% confidence interval [CI] 60-99%). Also, the results suggested that protection afforded by vaccination against Hib extended to the family members of vaccinated children, School attendance was found to be protective against invasive Hib disease (OR : 0.33; CI : 0.14-0.75). Cases more often than controls reported sufferring from asthma and allergies (OR : 4.8; CI : 1.2-19.4). Conclusions. Post-licensure vaccine efficacy is high among children greater than or equal to 2 years of age, The observed association between asthma and epiglottitis is novel and deserves further investigation.