STAT news reports on the myriad theories surrounding whether H1N1 flu vaccines could have triggered a neurological sleep disorder.

“We don’t know if there’s an association or not for sure. I believe there is, even though the study I did showed that there wasn’t,” Black, an infectious diseases expert at Cincinnati Children’s Hospital, told STAT.

“The upshot of this is that this is a complicated story,” he said. “But I think the real upshot is we need to figure this out because there will be another pandemic.”