Microbiota development in early life mediates association between mode of delivery and vaccine responses

The gut microbiota in early life, when critical immune maturation takes place, may influence the immunogenicity of childhood vaccinations. We assessed the association between mode of delivery, gut microbiota development in the first year of life, and mucosal antigen-specific immunoglobulin G (IgG) responses against pneumococcal and meningococcal conjugate vaccination at ages 12 and 18 months, respectively, in a prospective birth cohort of 120 infants. Birth by natural delivery was associated with higher IgG responses against both vaccines, which for the anti-pneumococcal IgG response could be explained by a gut microbial community composition with high abundances of Bifidobacterium and Escherichia coli in the first weeks of life. High E. coli abundance in the same period was also associated with higher anti-meningococcal IgG responses. Our results suggest that associations between mode of delivery and antibody responses to routine childhood vaccines are mediated by gut microbiota development.