Gut bacteria protein linked to fever after COVID-19 vaccines

A study published in the journal Science suggests that a protein produced by gut bacteria may be linked to fever and flu-like symptoms following mRNA COVID-19 vaccinations. Researchers, including those from the Max Planck Institute for Biology Tübingen, tracked 171 healthy adults to investigate why immune responses vary significantly between individuals.

The research found that individuals who experienced higher temperatures after vaccination had gut microbes that produced more flagellin, a protein used by bacteria for movement. Specifically, members of the Lachnospiraceae bacterial family were associated with higher flagellin gene activity and increased low-grade inflammation in blood and stool samples prior to vaccination.

The researchers propose that a steady supply of flagellin keeps the immune system primed, causing a stronger inflammatory response when a vaccine is administered. Notably, the study indicated that these inflammatory reactions and dietary factors did not appear to affect the effectiveness of the vaccine's antibody response, suggesting that side effects may not compromise immunity.