Genetic factors may have contributed to a spike in narcolepsy cases observed among children in Finland who received the swine flu vaccine Pandemrix, the World Health Organization said Tuesday.
A WHO expert panel says of 22 narcolepsy patients tested, all had a gene commonly associated with narcolepsy, a disorder that causes people to suddenly fall asleep but is rarely fatal.
About 30 percent of people in Finland have that particular gene, compared with 15 percent in the rest of Europe, said Patrick Zuber, WHO's top vaccine safety official.
Last week, Finnish authorities said they had found a nine-fold increased risk of narcolepsy among 4- to 19-year-olds who were given the swine flu shots. In total, 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.
Lesser increases were also observed in Sweden and Iceland, WHO said.
WHO's Global Advisory Committee on Vaccine Safety said in a statement Tuesday that it agreed with Finnish authorities that there was a "strong association" between the vaccination, the genetic makeup of the patients, and the narcolepsy cases.
But since a coincidental correlation cannot be ruled out, and as narcolepsy after swine flu vaccination has been reported in only a few countries so far, the panel recommended that Pandemrix continue to be administered to children.
To date, at least 12 countries have informed Pandemrix's British manufacturer GlaxoSmithKline PLC of narcolepsy cases following vaccination.
WHO declined to say which other countries apart from Sweden, Finland and Iceland, had reported cases, citing rules requiring the global body to be formally notified by its member state's governments before publicly naming affected nations.
But it said the three countries identified had "notably higher" instances than the other nine.
A spokesman for GlaxoSmithKline was unable immediately to provide the information.