Study: China’s Narcolepsy Cases Unrelated To H1N1 Vaccine
New research shows that the occurrence of narcolepsy in China peaks in April, five to seven months after the peak flu season, but the flu vaccine is unlikely the cause of the increase.
AsianScientist (Aug. 23, 2011) - Narcolepsy is a chronic neurological disorder that is caused by a loss of hypocretin - a neurotransmitter in the brain that is responsible for communication of biological processes, such as sleep. When brain cells lose hypocretin there is an inability to control sleep-wake cycles.
Less than one percent of the world population have the disorder and affected individuals experience sudden bouts of sleep at any time, a sudden loss of voluntary muscle tone (cataplexy), vivid dreams or hallucinations, and short periods of total paralysis.
New research shows that the occurrence of narcolepsy in China is highly correlated to a seasonal pattern, with onset most frequent in April. A significant increase in narcolepsy cases was also observed following the 2009-2010 H1N1 pandemic, but the findings show that flu vaccination was unlikely the cause of the increase.
For the present study, the research team, led by Dr. Fang Han from the Beijing University People's Hospital in China and Dr. Emmanuel Mignot with the Stanford Center for Sleep Sciences and Medicine in the US, conducted retrospective analysis of narcolepsy onset in patients diagnosed between 1998 and 2011 in Beijing.
Data on the month and year of narcolepsy onset was collected from 629 patients (86 percent of whom were children) who were part of the Stanford-Beijing University Chinese narcolepsy study cohort. A vaccination history was provided by 182 participants who developed narcolepsy after October 2009.
"Our findings show a seasonal variation in narcolepsy onset in a Chinese population, occurring most frequently in late spring and early summer," said Dr. Han.
Analysis revealed that the onset of narcolepsy was least frequent in November and occurred most often in April, with close to a seven-fold increase from lowest point to peak time.
Researchers also studied year-to-year variations, identifying 173 cases of narcolepsy following the 2009-2010 H1N1 flu pandemic which represented a three-fold increase in the disorder. A five to seven month delay between the seasonal peak in flu and peak in the onset of narcolepsy was also observed.
"The increase in narcolepsy incidence was unlikely caused by increased vaccination as only six percent of study narcolepsy participants reported receiving a vaccination against H1N1," noted Dr. Mignot, a professor of psychiatry and behavioral sciences.
However, Mignot conceded it is possible that the strong immune response prompted by the Pandemrix vaccine increases the risk of narcolepsy. He emphasized, however, that more study is needed and that people should not avoid getting vaccinated.
“Even with Pandemrix, it’s still a very small risk - and there’s a bigger risk from dying of an infection if you don’t get vaccinated,” he said.
The article can be found at: Han F. et al.(2011) Narcolepsy onset is seasonal and increased following the 2009 H1N1 pandemic in China.
Source: Stanford School of Medicine.
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