Carriage of Haemophilus influenzae in the Pre- and Post-Hib Vaccine Eras Revisited: A Systematic Review and Meta-Analysis

Background/Objectives: Re-emergence of Haemophilus influenzae serotype b (Hib) was reported in several European countries. We aimed to characterize the age distribution of H. influnezae carriage before and after Hib vaccination. Methods: We conducted a systematic review and meta-analysis to reassess H. influenzae carriage dynamics in the pre- and post-Hib vaccination eras, focusing on age-specific patterns in childhood. Searches were performed with no date restriction and included PubMed/MEDLINE, Scopus, Web of Science, WHO Global Index Medicus, and the Cochrane Library. Eligible studies reported nasopharyngeal and/or oropharyngeal carriage prevalence and serotype distribution. Pooled estimates with 95% confidence intervals (CIs) were calculated using random-effects models, with age-stratified analyses. Results: Twenty-two studies were included (12 pre- and 10 post-Hib vaccination). Pre-vaccination, pooled H. influenzae carriage prevalence was 24.3% (95% CI, 18.9–30.7%), including 6% (95% CI, 3.4–12.8%) for Hib and 17.5% (95% CI, 12.6–23.9%) for non–type b strains. Post-vaccination, overall carriage remained similar (21.8%; 95% CI, 14.6–31.2%), but Hib carriage declined markedly to 0.67% (95% CI, 0.26–1.71%), while non–type b strains predominated (16.7%; 95% CI, 10.4–25.6%). Meta-analysis showed that carriage peaked around 4–5 years of age and persisted into later childhood. Conclusions: Hib vaccination has reduced Hib carriage, but overall H. influenzae carriage persists due to non–type b strains. Age-related persistence of carriage may have implications for herd protection, particularly in the context of evolving vaccination schedules with early childhood boosters. Continued surveillance integrating carriage and immunological data is needed to inform optimization of vaccination strategies.