Does the gut microbiota influence vaccine efficacy?

Vaccines are one of the greatest successes of public health, saving millions of lives worldwide, especially among young children (0-5 years), who are more vulnerable to infectious diseases. However, their efficacy varies from one population to another, with higher rates of protective immunity in European countries than in low- and middle-income countries (LMIC). Since the development of the gut microbiota in early life is intimately linked to the maturation of the immune system, and the microbiota of children in LMIC differ significantly from those of European children, researchers reviewed the evidence pointing to the gut microbiota’s role in disparities in vaccine response.

Immunomodulatory properties

A study on vaccines against tuberculosis, tetanus, hepatitis B, and poliomyelitis in Bangladeshi infants found that the presence of certain taxa is correlated with the rate of vaccine response, positively in the case of Actinobacteria, but negatively for Enterobacteriaceae. In addition, interventions to modify the microbiota (prebiotics, probiotics, antibiotics) provide further evidence of its involvement in vaccine response. A 2018 systematic review summarized the results of 26 studies in humans that used probiotics to enhance the efficacy of various vaccines. The review found positive outcomes in half the studies. Conversely, studies investigating the effects of antibiotics found either no improvement or a reduced immune response, which was attributed to disruption of the microbiota.

Two bacterial genera especially involved 

Two bacterial genera seem particularly capable of modulating responses to vaccines. Bifidobacterium and Bacteroides are essential for the development of a healthy microbiota in young children. However, young children can face significant microbiota disruptions (cesarean section, etc.). The effects of the microbiota on vaccine responses appear to be mediated by certain metabolites and/or cellular components, such as short-chain fatty acids, exopolysaccharides, or extracellular vesicles.

Towards a new generation of vaccine strategies

Although the relevant strains and products need to be better characterized, the intricate relationship between the microbiota and vaccine efficacy opens up rich clinical perspectives. This includes new vaccine stimulation therapies able to improve protection for children from LMIC without the use of adjuvants, which are often thought to have adverse side effects.