We know that vaccines are often not as effective in developing nations as they are in industrialized nations and a recent study published in September in Immunity may provide insight into why this discrepancy exists. Researchers in the US and Brazil examined a possible link between the microbiome and the effectiveness of vaccines.

Previous research had shown that expression of TLR5, a cell-surface receptor for bacterial flagellum, correlates with TIV (a popular flu vaccine) vaccination antibody response in humans. In this study, researchers observed this correlation between TLR5 expression and the immune response from the TIV vaccine through a series of experiments.

First, researchers found evidence to suggest that the correlation between TLR5 and antibody response is not because of any kind of contamination in the vaccine. They also saw a significant decrease in antibody response in mice with a mutated TLR5 gene, when they were given the TIV vaccine, even though they showed no prior immunodeficiency. Other evidence was found to suggest that the gut microbiome is necessary for a rapid antibody response after vaccination, because the response of antibody secreting cells depends on the microbiome. Research also suggested that multiple types of bacterial communities are necessary, and not just a few specific species, for gut bacteria to mediate immune responses.

These findings of the microbiome’s role on the effectiveness of a vaccine in inducing an immune response could impact future vaccine development. Further research may be done to better understand the role that diet, health, and other factors that affect the human microbiome play in vaccine response. Microbiome differences between individuals in developing nations and those in industrialized nations could play a significant role in the efficacy of existing and future vaccines.