Why do some people get the flu after the flu shot? The answer may be in the gut. While studying gene expression and the strength of the immune response in people infected with influenza vaccine, Oh et al. found a surprise: The gene that codes for the protein toll-like receptor 5 (TLR5) which is linked to gut bacteria, was also linked to strong immune response. The team gave flu vaccine to mice, some engineered to lack gut microbes and some to lack the gene for TLR5. Seven days later, the mice had significantly reduced levels of vaccine-specific antibodies in their blood as compared with control mice, suggesting that bacterial signaling boosts the vaccine’s effect…..
