In spring last year, the number of narcolepsy cases in Beijing, China, multiplied threefold. Now, it looks like the swine flu pandemic of the previous winter was to blame.

Previously, similar rises in cases of narcolepsy – a disorder that causes sleepiness at inappropriate times – have been linked to use of a swine flu vaccine. The cause was presumed to lie in the drug’s adjuvants – additives that boost the immune response to the vaccine.

The claim puzzled researchers who saw a concurrent rise in narcolepsy cases in China, where few people had opted to get vaccinated and those who did received a vaccine without adjuvants. Could the flu itself be to blame?

To find out, Fang Han and his colleagues at Beijing University People’s Hospital studied the medical profiles of 906 people who had come to the hospital with narcolepsy since 1998.


The group found that, even in the years before the vaccine was introduced in October 2009, the number of narcolepsy cases followed a seasonal pattern – cases dropped significantly around November and spiked in April. The peak was higher than normal in the spring after the swine flu pandemic (Annals of Neurology, DOI: 10.1002/ana.22587).

Big red flag

The idea that flu causes narcolepsy fits in with the theory that narcolepsy is triggered by the immune system’s response to airway infections.

“There is no way to definitively say that the [swine flu virus] caused narcolepsy, but we think this raises a big red flag,” says Juliette Faraco at Stanford University’s Center for Narcolepsy in California, a co-author of the study.

The flu vaccine will protect against the flu – if it also protects against narcolepsy, all the better, she says.