The team has two main hypotheses for why individuals may struggle to recover after infection with COVID-19. First, the researchers believe that some individuals with long COVID-19 might be experiencing a persistent virus infection, and the vaccine can provide relief because it induces a response in the body that gets rid of the lingering virus. Second, they believe that long COVID-19 in others might be driven by autoimmune disease. In those instances, the vaccine might be making people feel better by inducing the production of certain kinds of cytokines, or the vaccine may be worsening symptoms by exacerbating autoimmune responses. “We are really trying to get to the bottom of why people are suffering,” Iwasaki said.