The European Medicines Agency said Friday it was probing whether there is a link between the Pandemrix swine flu vaccine and the sleeping disorder narcolepsy amid concerns in Finland and Sweden.
"The European Medicines Agency has launched a review of Pandemrix on the request of the European Commission to investigate whether there is a link between cases of narcolepsy and vaccination with Pandemrix," the EMA said.
"A limited number of cases was reported, all collected through spontaneous reporting systems, mainly in Sweden and Finland," the London-based agency added in a statement.
Finland's National Institute for Health and Welfare on Tuesday recommended halting the use of Pandemrix until a probe into a possible link to narcolepsy among children is concluded.
Last week, neighbouring Sweden's Medical Products Agency also opened an inquiry into the Pandemrix vaccine following reports of young people having developed symptoms consistent with narcolepsy after getting their shot.
Narcolepsy is a condition in which sufferers suddenly fall into a deep sleep.
"Its precise cause is unknown, but it is generally considered to be triggered by a combination of genetic and environmental factors, including infections," the EMA said.
It added that Pandemrix - produced by British pharmaceutical company GlaxoSmithKline - has been used since September 2009 for vaccination against H1N1 influenza for at least 30.8 million Europeans.