Effectiveness of 2+1 PCV7 vaccination schedules in children under 2 years: a meta-analysis of impact studies.

Although a case control study suggested high effectiveness of the 2+1 PCV-7 vaccination, schedule against invasive pneumococcal disease (IPD) in children the results of impact studies in, different countries yield considerable differences in the magnitude of the effects. A systematic, literature review was conducted to identify all relevant studies on IPD incidence reduction after onset, of PCV7 vaccination programmes in children younger than 2 years of age given in the 2+1 schedule. The incidence rate ratio between IPI incidences for vaccine serotypes before and after beginning of the, vaccination programme was calculated for each study. Heterogeneity was assessed and attempts to, identify causes for heterogeneity were made. In the literature search 4 studies which fulfilled inclusion, criteria were identified. The summary estimates yielded an IRR 0.10 [0.04; 0.30] suggesting a 90%, incidence reduction. Heterogeneity was high with I(2)=93%. Heterogeneity might be explained by, differences in vaccination rates, the way vaccination rates were assessed, matching of the periods of, vaccination and case ascertainment, time between onset of the vaccination programme and onset of, case ascertainment during the vaccination period and the length of the observation period after onset, of the vaccination programme. A study which started 3 years after onset of the vaccination programme, with vaccination rates ≥80% throughout the ascertainment period of the incidence rates reported a, 98% reduction in the incidence rates. A meta-analysis on IRR studies on reductions of the IPD, incidence in children <2 years of age suggested high effectiveness of the 2+1 vaccination schedule for PCV 7.