A flu vaccine administered in Europe around 2009-2010 was associated with an increased risk of narcolepsy.

“The worst-case scenario that we've seen so far was a flu vaccine that was, it was a regular flu vaccine, it was not an mRNA, it was not a DNA, it was just a regular flu vaccine that was administered in Europe a number of years ago. This is back in 2009, 2010. And they did find an increased risk of narcolepsy in patients that were vaccinated with that type of vaccine. And the thought process there was that perhaps there was an immune response that cross-reacted with the portion of the brain that produces hypocretin, which is the basis for narcolepsy.”