In 2010, following the H1N1 pandemic and the vaccination campaign to reduce its impact, researchers noted a significant increase in a rare neurological disorder, narcolepsy, in Sweden and Finland. Since then researchers have been studying a possible association between a specific H1N1 flu vaccine, Pandemrix by Glaxo-Smith-Kline (GSK) and a sudden onset of the sleep disorder narcolepsy. In those two countries the association seems strong, but the full story is still complicated with many unknowns.
Narcolepsy is a neurological disorder marked by excessive sleepiness, cataplexy (sudden loss of muscle tone, usually triggered by emotions) and disordered sleep. Almost all cases are associated with low levels of hypocretin in the hypothalamus – this is a hormone involved in sleep regulation. Further there is a strong HLA (human leukocyte antigen) association – specifically DQB1*0602. HLA is a group of proteins involved in regulating immune activity. An HLA association strongly suggests that narcolepsy may be an auto-immune disease.
The current synthesis of this information is that narcolepsy occurs in genetically susceptible individuals after some environmental trigger, such as in infection, that causes the immune system to attack and destroy hypocretin cells in the brain.