In 2010 the number of Finnish children with narcolepsy took a steep climb, prompting an investigation into the H1N1 flu vaccine, Pandemrix.
Hanna Nohynek of the National Institute for Health and Welfare in Finland and Markku Partinen of the Helsinki Sleep Clinic studied the narcolepsy increase from 0.31 incidents per 100,000 children during 2002-2009 to 5.3 cases per 100,000 children in 2010. The incidence rates for adults were unchanged, leading the researchers to suspect something environmental or chemical as the causative agent.
Suspecting the widely used vaccine, researchers went back through vaccination and health records on children born between 1991 and December of 2005. They compared the vaccination and health records of these individuals and discovered unvaccinated children were 13 times less likely to have narcolepsy.
Study authors concluded the evidence was enough to link Pandemrix to the spike in narcolepsy cases during the H1N1 pandemic, as reported by Medical News Today.