Baseline Analysis of Serotype-Specific IgG Antibody Levels for 13-Valent Pneumococcal Conjugate Vaccine in Healthy Chinese Individuals: A Multicenter Retrospective Study.

BACKGROUND/OBJECTIVES: The immunogenicity of Streptococcus pneumoniae vaccines is commonly evaluated by assessing the fold increase or proportions exceeding 0.35 μg/mL in serotype-specific IgG antibody levels post-vaccination. Establishing baseline antibody levels in unvaccinated populations is therefore essential for defining serological thresholds and understanding naturally acquired immunity. This study aimed to assess the seroprevalence and baseline levels of IgG antibodies specific to 13 pneumococcal capsular polysaccharide serotypes in healthy infants and young children across multiple regions of China from 2016 to 2023, supporting evidence-based PCV13 vaccination strategies.

METHODS

IgG concentrations for 13 serotypes (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, and 23F) were measured in unvaccinated individuals using the WHO-recommended ELISA. Univariate and multivariate analyses were applied to evaluate regional, age, and gender effects on baseline antibody levels.

RESULTS

GMCs for serotypes 6B, 14, 19A, and 19F exceeded 0.35 μg/mL, with 14 being the highest (1.64 μg/mL) and serotypes 3 and 4 the lowest. Significant regional variation ( < 0.001) and a U-shaped age trend were observed, with the lowest being at 7-11 months ( = 0.003).

CONCLUSIONS

Baseline IgG levels varied by region and age. No significant gender differences were observed, and overall antibody levels were higher in the southern region.