Why do some people spend the day after a vaccine on the couch with a fever while others feel nothing? A new study in the journal Science points to an unexpected factor: a protein made by certain gut bacteria.
Researchers led by the Max Planck Institute for Biology Tübingen in Germany found that adults who ran higher temperatures after mRNA COVID-19 vaccines had gut microbes that produced more flagellin, the protein bacteria use to build the whip-like tails that help them move. The study tracked 171 healthy young adults, most of whom were receiving a third mRNA dose.
