Post-vaccination hypersomnia - occurrence of idiopathic hypersomnia and narcolepsy type 2 after Pandemrix vaccination in a case- series from Sweden and Finland.

Background: The swine flu (H1N1) pandemic of 2009-2010 witnessed an increase in reported cases of narcolepsy, clearly demonstrated in children developing narcolepsy type 1 in several countries, most notably Sweden and Finland. This increase has been attributed to the Pandemrix vaccination.

Objective: We performed an inventory of a case -series of patients displaying the onset of excessive daytime sleepiness close to the Pandemrix vaccination who did not suffer from narcolepsy type 1 but other types of central hypersomnia, such as idiopathic hypersomnia and narcolepsy type 2.

Results: In Sweden and Finland, nine patients were identified, and their sleep investigations were scrutinized to fulfill the diagnostic criteria. There were six female and three male patients, three with narcolepsy type 2 and six with hypersomnia.

Discussion: The results do not include epidemiologic risk calculations and should therefore be interpreted cautiously. We plan to follow up this study with analyses of blood samples for possible genetic risk factors other than HLA.