Scientists think they may have started to unravel the link between the influenza vaccine and narcolepsy, shedding precious light onto how the Pandemrix vaccine given in the 2009/2010 swine flu outbreak put children at an increased risk of developing the involuntary sleep disorder.
At least 900 cases of narcolepsy associated with the vaccine have so far been reported in Europe, with the UK government conceding in September that this particular swine flu vaccine could, on rare occasions, trigger the disorder.
But the question still remains: how could the GSK vaccine – which was given to 31 million people across Europe before it was withdrawn – cause narcolepsy? Now scientists at Stanford University School of Medicine think they may have the answer: molecular mimicry.
Researchers reporting in Science Translational Medicine examined 39 cases of narcolepsy in children, finding that the affected childrenâ€™s CD4 cells reacted both to hypocretin – a neurotransmitter involved in wakefulness – and a part of the HA surface protein of the 2009 H1N1 pandemic flu virus. In contrast, the CD4 cells of the childrenâ€™s unaffected siblings didnâ€™t react to either.
Hypocretin is central to the pathogenesis of narcolepsy, as the disorder develops when the immune system destroys hypocretin-producing neurons in the hypothalamus. Therefore this cross-reactivity of T cells primed to attack the HA surface protein of H1N1 gives an insight into a possible mechanism for how Pandemrix could have interacted with hypocretin cells in the brain and led to the rare cases of narcolepsy.