Results from a Swedish registry based cohort study indicate a 4-fold increased risk of narcolepsy in children and adolescents below the age of 20 vaccinated with Pandemrix, compared to children of the same age that were not vaccinated. The results are in line with those of a similar Finish registry study.
The Agency (MPA) has in co-operation with the healthcare regions of Skåne and Västra Götaland, the county councils of Östra Götaland and Stockholm and with the Karolinska Institutet performed a study of a possible relationship between vaccination with Pandemrix and the occurrence of narcolepsy.
All cases of diagnosed narcolepsy reported to the healthcare databases in these four regions between October 1st 2009 and December 31st 2010 have been linked to information in the regional vaccination databases. These four regions have around 5.3 million inhabitants, which corresponds roughly to 57 percent of the Swedish population. The vaccination coverage was on average 67 % for children and adolescents under the age of 20 and 51 % for adults.
The study shows a 4-fold increased risk for children and adolescents vaccinated with Pandemrix to be diagnosed with narcolepsy as compared with unvaccinated subjects (4,06 cases per 100 000 person years in vaccinated children/adolescents compared with 0,97 cases per 100 000 person years in unvaccinated). This risk would translate into an absolute risk of three cases of narcolepsy in 100 000 vaccinated children/adolescents. No increased risk was seen in adults.