The influence of the intestinal microbiome on vaccine responses.

There is substantial variation between individuals in the immune response to vaccinations. The intestinal microbiome plays a crucial rule in the development and regulation of the immune system and therefore its composition might affect how individuals respond to vaccinations. In this review, we summarise studies that investigated the influence of the intestinal microbiome on humoral and cellular vaccine responses. To date, only four studies (three in infants and one in adults) have investigated the influence of the intestinal microbiome on vaccine responses. All found an association between the intestinal microbiome and vaccine responses. Despite the heterogeneity in study designs (including different vaccines, schedules, timing of collection of stool and blood samples, analysis methods and reporting of results on different taxonomic levels), findings across studies were consistent: a higher relative abundance of the phylum Actinobacteria (oral and parenteral vaccines) and Firmicutes (oral vaccines) was associated with both higher humoral and higher cellular vaccine responses, while a higher relative abundance of the phylum Proteobacteria (oral and parenteral vaccines) and Bacteroidetes (oral vaccines) was associated with lower responses. Further, well-designed, adequately powered studies using whole-genome sequencing (to include the influence of viruses, fungi and parasites) are needed to investigate in more detail the influence of the intestinal microbiome on vaccine responses. This will help identify strategies to improve vaccine efficacy and duration of protection, particularly in infancy when the intestinal microbiome is more amenable to external influences and plays an important role in the development of the immune system.