Swine flu, not vaccine, may trigger narcolepsy
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 vaccine’s adjuvants, additives that boost a person’s immune response to the shot.
The claim puzzled researchers who saw a rise in narcolepsy cases in China, where few people had opted to get vaccinated and those who did received a vaccine without adjuvants. Some began to suspect that the flu itself was to blame.
To find out, Fang Han and his colleagues at Beijing University People’s Hospital looked at the medical profiles of 906 people who had come to the hospital with narcolepsy since 1998.
The team found that, even before the vaccine was introduced in October 2009, the number of narcolepsy cases followed a seasonal pattern, dropping significantly around November and spiking in April. The peak was higher than normal in the spring after the swine flu pandemic (Annals of Neurology, DOI: 10.1002/ana.22587).
The idea that flu causes narcolepsy fits in with the theory that the sleep disorder is triggered by the immune system’s response to airway infections, says Masashi Yanagisawa at the University of Texas Southwestern Medical Center in Dallas, who was not part of the study. However, he adds that there is “no direct cellular evidence” to support the idea yet.
Study co-author Juliette Faraco at Stanford University’s Center for Narcolepsy in California agrees that a direct link between swine flu virus and narcolepsy has yet to be established, “but we think this [study] raises a big red flag”.