Update on the investigation of narcolepsy cases in Sweden
Friday, September 10, 2010
The investigation of a possible relationship between Pandemrix and reported cases of narcolepsy is currently ongoing in Sweden and several other EU-countries. So far 22 cases have been reported by the Swedish health care system and MPA is currently trying to assess back ground incidence of narcolepsy. Together with this update the MPA also provides a document describing how the overall investigation is being performed.
The MPA has up to September 2nd received 22 reports of narcolepsy from the healthcare system. In addition we have received 13 reports directly from patients or parents which have not been reported via the healthcare system. In the current investigation of the narcolepsy cases reported to the MPA it is important to understand if the reported number of cases of narcolepsy is higher than what could be expected in the population.
Expected cases of narcolepsy in the population compared to reported cases
Approximately 100 individuals have been diagnosed with narcolepsy each year in Sweden according to the data that the MPA has received from the National Board of Health and Welfare. The main part of these cases is diagnosed in the 20-40 years of age group. The last six years 7-16 cases have been diagnosed per year in persons below the age of 20.
Approximately a 65 percent share of all children in Sweden (younger than 18 years of age) is estimated to have been vaccinated with Pandemrix. The estimation is founded on statistics from the Stockholm population. In this group it is expected (from the numbers above and during a time period that corresponds to October 2009 to August 2010) that less than 10 children would have been diagnosed with narcolepsy. This should be compared to the 22 reports of narcolepsy after vaccination received by the MPA from the healthcare system and the 13 reports directly from patients not reported through the healthcare system. Of these there are 20 cases concerning children and adolescents below 18 years of age in the reports from the healthcare system and 10 cases from the consumer reports, respectively.
Thus, the number that now has been reported is higher that expected comparing data from previous years.
Occurrence of cases of narcolepsy in the Stockholm County
The database registering visits in out and in-patient care in the Stockholm County, with a population of approximately 2 million, may also be used to estimate the number of patients who were diagnosed with narcolepsy in different age groups. Regarding children younger than 18 years of age, there were no or isolated cases registered during the years 2005 to 2009, while 6 cases were registered during 2010. In total during the pandemic period 16 cases of narcolepsy were diagnosed (10 adults and 6 children, younger than 18 years of age). Thus, from these statistics an increase in the total number of narcolepsy cases was noted in the entire population of Stockholm during 2010.
Cases of narcolepsy in vaccinated individuals compared with non-vaccinated in Stockholm
All individuals vaccinated with Pandemrix in the Stockholm County were included in a designated registry (Vaccinera). In total 1.1 million individuals were included, corresponding to 54% of the population in Stockholm.
Sixty-five percent of all children and adolescents (younger than 18 years of age) have been vaccinated in Stockholm. Of the six cases of narcolepsy that were reported in this age group, four belong to group which has been vaccinated. Two of the six children belong to the non-vaccinated group. Among the 10 narcolepsy cases where the patients are older than 18 years of age, five were in the vaccinated part (50%) and five in the other half of the population that was not vaccinated. Calculations of these numbers show that the occurrence of narcolepsy does not seem to differ between vaccinated children or adults compared to non-vaccinated.
The first part of the investigation of the narcolepsy cases shows that the number of cases of narcolepsy in the population has increased in Sweden as well as in the Stockholm County. Concomitantly, data from Stockholm indicates that the increase seems to be of the same magnitude in those vaccinated as in those not receiving any vaccine.
Since the results from the Stockholm data are based on small number of cases they must be interpreted with caution. The inventory of all new cases that now is taking place in Sweden is expected to yield important new information.
More information about the current investigation is given in the document “Approaches to investigate a possible relationship between reported cases of narcolepsy and vaccination with Pandemrix“– please see link to the right.