Impact of Haemophilus influenzae type b conjugate vaccination on hospitalization for invasive disease in children fifteen years after its introduction in Italy

In Italy, Hib conjugate vaccine was introduced for infants in 1999 and included in the DTaP-HBV-IPV-Hib combination in 2001, with an uptake of 83.4% in 2002, >90% by 2005, and >95% by 2011. We estimated the impact of Hib vaccination on hospitalizations for H. influenzae invasive disease in children <5years. Age-specific hospitalization rates and hospitalization risk ratios (HRRs) with 95%CI during 2001-2013 were calculated performing time-series analysis. The number of cases reported to the national surveillance of invasive bacterial diseases was compared to the number of hospitalizations between 2007-2013. Hospitalization rates declined from 2.3 in 2001 to 0.9×100,000 in 2002 (HRR=0.4, 95%CI=0.3-0.6, p<0.05) among children 1-4years and from 5.4 in 2001 to 2.4×100,000 in 2005 (HRR=0.4, 95%CI=0.2-0.9, p<0.05) among infants. During 2007-2013: 401 cases were reported, 242 were typed, 12.4% were by serotype b; 861 hospital admissions were recorded. Applying the percentage of typed b strains retrieved from the surveillance to the number of hospitalizations for invasive H. influenzae disease, an estimated 107 episodes could be attributable to serotype b. These findings provided reassuring data on the impact of Hib vaccination on the burden of hospitalization for invasive disease in Italian children.