The influence of probiotics on vaccine responses – A systematic review

The immunomodulatory effects of probiotics may influence the response to vaccines. We systematically reviewed prospective randomised placebo-controlled studies in humans that have investigated the effect of probiotics on humoral vaccine responses. We found 26 studies, involving 3812 participants, investigating the effect of 40 different probiotic strains on the response to 17 different vaccines. A beneficial effect of probiotics was reported in about half of the studies. The evidence for a beneficial effect of probiotics on vaccine response was strongest for oral vaccinations and for parenteral influenza vaccination. However, there was substantial variation between studies in the choice of probiotic, strain, dose, viability, purity, and duration and timing of administration. The one study that investigated the effect of probiotic administration to mothers during pregnancy found lower vaccine responses in their infants. The studies in our review suggest that probiotics offer a relatively cheap intervention to improve vaccine efficacy and duration of protection. Future studies should focus on establishing optimal strains, doses and timing of administration in relation to vaccination.