Since August 2010, following widespread use of vaccines against influenza (H1N1) 2009, cases of narcolepsy, especially in children and adolescents, have been reported. Narcolepsy is a rare sleep disorder that causes a person to fall asleep suddenly and unexpectedly. The rates reported from Sweden, Finland and Iceland have been notably higher than those from other countries. Swedish and Finnish authorities have presented preliminary statements on their investigations in the first quarter of 2011.
On 1 February 2011, the National Institute for Health and Welfare of Finland issued a preliminary statement following an investigation into the cases of narcolepsy in Finland1 . A systematic retrospective registry-based review was conducted of all new narcolepsy cases diagnosed during 2006-2010. Cases from 2009-2010, who were born in 1990 or later, were reviewed using newly developed Brighton collaboration criteria for the disease. During 2009-2010 they found that the risk of narcolepsy among people aged 4-19 years old who had received pandemic influenza vaccine was nine times higher than that among those who had not been vaccinated. This corresponds to a risk of about 1 case of narcolepsy per 12,000 vaccinated in this age group. No increased risk has been seen in younger or older age groups.