Cross-sectional analysis of pneumococcal conjugate vaccine immunity in infants from the community

BACKGROUND: Pneumococcal conjugate vaccines (PCV) reduce invasive disease and routine pediatric infections, yet subtherapeutic antibody responses have been reported in children with refractory otolaryngologic disease. This study evaluated pneumococcal antibody responses in a community cohort of vaccinated children and compared findings with prior specialty cohorts and prelicensure trial data. METHODS: Serum from children aged 15-36 months with a documented four-dose PCV series was analysed for IgG concentrations to 14 serotypes. Protective thresholds were defined for invasive disease (≥0.35 μg/ml) and noninvasive disease (≥1.3 and ≥ 2.0 μg/ml). Results were compared with published pediatric cohorts and prelicensure trial data. RESULTS: Overall, 77.1% of children met the invasive disease threshold. Only 31.3% and 18.8% met the ≥1.3 and ≥ 2.0 μg/ml thresholds, respectively. Antibody levels were consistently lower than those reported in prior cohorts and prelicensure trials across most serotypes. CONCLUSIONS: These findings suggest that real-world immunogenicity following routine PCV may differ from that observed in strictly defined and controlled clinical trial populations, particularly at higher antibody thresholds associated with noninvasive disease. Larger-scale, prospective studies are needed to determine if trends hold across broader cohorts.