Finland's National Institute for Health and Welfare (THL) has confirmed that swine flu shots that increased risk of narcolepsy in children also had the same effect in adults.
The THL says that the Pandemrix vaccine used in 2009 and 2010 increased adults' likelihood of falling ill with the disease by three to five times. This was lower than the risk for children and youth, though.
The study will force a re-evaluation of state funding for care of grown-ups who developed the illness.
The THL says that most of the adults who came down with narcolepsy between 2009 and 2011 were under the age of 40. The risk of developing the debilitating illness after the H1N1 jab returned to pre-vaccination levels within eight months.
During that period, 25 adults fell ill with narcolepsy, with all but two under 40 years of age, and all under age 65.
Swine flu still kills in Finland -- old shots still 50% effective
The research backs up results from earlier studies that indicated a higher risk of narcolepsy in vaccinated adults in Sweden and France.
The THL says that Pandemrix prevented a swine-flu epidemic in Finland in the winter of 2009-10. About half of the population were inoculated. The agency estimates that the shots prevented 80,000 swine flu infections, as well as approximately 50 deaths caused by the influenza A(H1N1) virus.
This remained the most common flu virus in Finland this past winter, causing 14 deaths. The THL reckons that the 2009-10 shots still provide more than 50 percent protection against the bug.