A study in Finland has found that children vaccinated against the H1N1 swine flu virus with Pandemrix were more likely to develop the sleep disorder narcolepsy.
The condition causes excessive daytime sleepiness and sufferers can fall asleep suddenly and unintentionally.
The researchers found that between 2002 and 2009, before the swine flu pandemic struck, the rate of narcolepsy in children under the age of 17 was 0.31 per 100,000.
In 2010 this was about 17 times higher at 5.3 per 100,000 while the narcolepsy rate remained the same in adults.
Markku Partinen of the Helsinki Sleep Clinic and Hanna Nohynek of the National Institute for Health and Welfare in Finland, also collected vaccination and childhood narcolepsy data for children born between January 1991 and December 2005.
They found that in those who were vaccinated the rate of narcolepsy was nine per 100,000 compared to 0.7 per 100,000 unvaccinated children, or 13 times lower.
The findings were published in the journal Public Library of Sciences One.
Pandemrix was the main vaccine used in Britain against the swine flu epidemic in which six million people were vaccinated.
It was formulated specifically for the swine flu pandemic virus and is no longer in use.
The World Health Organisation has conducted an investigation after the link was first suggested in Finland and Sweden two years ago and found no other countries experienced a increase in narcolepsy rates during or after the pandemic.
A spokesman for the UK regulator, the Medicines and Healthcare products Regulatory Agency, said: "The MHRA is aware of the study from Finland concerning Pandemrix vaccine and narcolepsy.
"The data from Finland, as well as from Sweden, were considered as part of an in-depth European safety review of Pandemrix in 2011.
"The outcome of this review was that Pandemrix may only be used in persons aged under 20 years if the annual seasonal vaccine was not available and if there was a particular need to immunise against H1N1. No restrictions on use in adults were imposed, and the EU review acknowledged the important role that Pandemrix played in reducing the consequences of H1N1 in Europe during the pandemic.
"Further work is ongoing to establish if a similar risk is evident in other countries where the vaccine was used. This includes a UK study led by the Health Protection Agency. The MHRA will review any new data as it becomes available."
Professor Sir David Salisbury, director of immunisation at the Department of Health, said: “The Department of Health is aware of the Finnish data, and keeps all new evidence under review.
"Through the MHRA and HPA, further UK research is going on into the risks associated with Pandemrix.
"This follows a European-wide review last year, which reached the conclusion that Pandemrix may only be used in people under 20 if the annual seasonal vaccine is not available and there is a particular need to immunise against H1N1.”