The immune system may have misidentified a protein in the vaccine
A team of scientists may have found a clue to why certain swine flu patients who had been administered an H1N1 vaccine in 2009 developed the sleep disorder, narcolepsy.
In a study released on Wednesday, the international team of researchers reported the problem may have been a case of mistaken identity by the immune system, according to a report by Time magazine.
Narcolepsy is an incurable disorder that interferes with normal sleep cycles, leaving people chronically sleepy during the daytime and prone to abruptly falling asleep. No one knows what causes it, although patients have very low levels of a brain chemical named hypocretin which is important for wakefulness. One theory is that a particular gene variant makes people susceptible, and that some environmental trigger pushes them over the edge.
A year after mass vaccinations began against a new strain of H1N1, some European countries like Finland, reported cases of narcolepsy in recipients of GlaxoSmithKline’s Pandemrix but not in people given other flu vaccines. Research found narcolepsy patients had that genetic predisposition, but no other explanation.
In the new study published in the journal Science Translational Medicine, Lawrence Steinman of Stanford University and colleagues found that the H1N1 virus contains a protein that is structurally similar to part of a brain cell receptor for the wakefulness chemical (hypocretin). They wondered if the flu-fighting antibodies generated by the Pandemrix vaccine might also latch on to those narcolepsy-linked receptors, leading to damage.
Doctors in Finland sent blood samples that had been stored from 20 people diagnosed with vaccine-associated narcolepsy. Seventeen samples harboured antibodies capable of reacting both to flu and to the narcolepsy-linked receptors. Recipients of another European vaccine, Novartis’ Focetria, didn’t harbour those cross-reactive antibodies.
Pandemrix contained much higher levels of the flu protein than Focetria, possibly because the two flu shots were made from different H1N1 subtypes, the researchers found.
However, the study doesn’t prove the link, Steinman stressed, since it is not yet clear how the antibodies could have gotten into the brain.
Moreover, some unvaccinated people who caught the flu also harbour the antibodies, he said, and a study from China found H1N1 infection itself may increase narcolepsy risk.
“It is a plausible theory,” William Schaffner, a flu vaccine expert at Vanderbilt University who wasn’t involved in the new research, told Time.
“Importantly, this would also appear to be a solvable problem, with manufacturing techniques to ensure that future vaccines don’t contain too much cross-reactive protein,” he said.
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