The institute's interim report on the association between the Pandemrix vaccine and narcolepsy shows that the risk of developing the sleep disorder among those vaccinated aged between four and 19 years old is nine times as high as for people in the same age group who have not received the vaccine.
In 2009 and 2010, 60 Finnish children and adolescents fell ill with narcolepsy. Of those who became ill, 52 (almost 90%) had received the Pandemrix vaccine.
The link is so obvious that it is unlikely that other confounding factors could explain the phenomenon instead, the institute said in a statement.
No cases were reported among those under four years of age and no increase the number of cases or the risk of falling ill with narcolepsy was observed among those above 19 years of age.
Finnish newspaper syndicate Vli-Suomen sanomalehdet last week quoted Terhi Kilpi, head of the vaccines department at THL, as suggesting that administering the vaccine to 5-20 year olds was perhaps a mistake. She was also quoted as saying that she would no longer recommend the vaccination to this age group.
The final report by the Finnish national narcolepsy task force will be released by the end of August.
In 2009, Sweden and Iceland also reported a surge in cases of narcolepsy when using a similar pandemic vaccine, THL said.
Further studies will pay close attention to infections and other stimuli associated with the pandemic vaccination and the possibility of joint effects will be explored, the institute stressed. The studies will aim in particular to clarify whether the immunological responses to the Pandemrix vaccine between young people with a genetic predisposition to narcolepsy differs from those who are not at risk.
EU safety review underway
Shortly after the Finnish and Swedish authorities began to report narcolepsy cases linked to the vaccine, the European Medicines Agency (EMA) launched a review of the vaccine, in autumn 2010.
An EMA spokesperson told EurActiv that the review is still ongoing and the issue was discussed in the agency's Committee for Medicinal Products for Human Use (CHMP) in September and November.
Based on current data the committee has not yet been able to conclude whether or not there is a link to narcolepsy. Therefore, "the safety signal for narcolepsy is still unconfirmed" and for the time being the benefit-risk balance of Pandremix remains positive, the spokesperson added.
The committee has asked for several new studies to gather more information before drawing up further conclusions on this. The Finnish study will be reviewed by the committee, probably at its meeting this month.
No date has been set for concluding the EMA review yet. The fact that narcolepsy seems to be restricted to very few countries remains "a big question mark for everybody" and "needs to be looked at very carefully," the spokesperson underlined.
The marketing authorisation for Pandremix is still valid.