Eight trials were included (300,297 children), but two of these analysed the same participants. Six of these were randomised controlled trials. Four were double-blind and an additional three had blinded outcome assessors. Adequate allocation concealment was reported by three trials.
The pooled estimates for vaccine efficacy against confirmed invasive Hib disease were 93% (95% CI 83 to 97; five studies) following three vaccine doses, 92% (95% CI 69 to 98, three studies) following two doses, and 59% (95% CI -20 to 86; three studies) following one dose. The effect was significant for two and three doses, but not for one dose. There was no significant statistical heterogeneity.
Efficacy against confirmed confirmed Hib meningitis was 88% (95% CI 46 to 97; two studies) following three vaccine doses, 92% (95% CI 37 to 99; three studies) following two doses and 62% (95% CI -29 to 89; three studies) following one dose. Again, the effect was significant for two and three doses, but not for one dose. There was no significant statistical heterogeneity.
The corresponding values for protection against confirmed Hib pneumonia were 91% (95% CI -66 to 99; one study) mid-point efficacy for two and three doses, and 67% (95% CI -44 to 93; two studies) for one dose. Vaccine efficacy after three doses against radiological pneumonia was 22% in two studies and -10% in one. The corresponding values were 2% and 26% for each of two studies for hospitalised pneumonia and 4% each for two studies that assessed clinical pneumonia. Overall, none of these results showed significant effectiveness for the respective outcomes. Only one study assessed clinical meningitis with mixed results (efficacy estimates between 1% and 84%).