HELSINKI (AP) - Finnish researchers have found an increased risk of narcolepsy among 4 to 19-year-olds who were given swine flu shots, a government health agency said Tuesday.
A preliminary study by the National Narcolepsy Task Force indicates that children vaccinated with Pandemrix "contributed to the observed increase in incidence of narcolepsy" compared to those who were not vaccinated in the same age group, it said.
The agency said, however, that the increase likely was caused "by joint effect of the vaccine and some other factor," and added that it would have to conduct more research as similar increases in narcolepsy cases have not been reported in other countries using the vaccine.
Pandemrix shots were made for the swine flu pandemic, and it is not clear how many people would still be receiving them since the usual flu shot now includes the swine flu strain. In Finland, health personnel stopped administering Pandemrix in August 2010 when concerns were first voiced about the vaccine.
Narcolepsy is a rare disorder that causes people to suddenly fall asleep. It is seldom fatal.
The National Institute for Health and Welfare said that 60 children and adolescents contracted narcolepsy in Finland in 2009 and 2010. Fifty-two of them - or almost 90 percent - had received the Pandemrix vaccine, it added.
It's not clear how many in the young age group were vaccinated with Pandemrix but half of Finland's 5.3 million population were given the shot during the winter of 2009 to 2010.
"Based on the preliminary analyses, the risk of falling ill with narcolepsy among those vaccinated in the 4-19 years age group was nine-fold in comparison to those unvaccinated in the same age group," the study said.
It found that the biggest increase was among those aged 5 to 15 years. No cases were seen among those under age 4 or over age 19.
The European Medicines Agency, the regulatory body responsible for authorizing use of the vaccine, launched an investigation into a possible link between the swine flu vaccine and narcolepsy in August.
GlaxoSmithKline PLC, which produces Pandemrix, said it was aware of the Finnish report.
"This investigation is independent of a broader ongoing European Medicines Agency investigation initiated in 2010," the company said in a statement. "GlaxoSmithKline is reviewing the report and believes it would be premature to draw any conclusions on a potential association between Pandemrix and narcolepsy until this European investigation has been completed."
The company said that more than 31 million doses of Pandemrix had been administered in 47 countries with 162 cases of narcolepsy reported in people who were vaccinated. Some 70 percent of the cases originated in Finland and Sweden, it said.
The World Health Organization welcomed the report but said it does not recommend any changes to use of Pandemrix and that the vaccine remains on the list of recommended vaccines.