Increased risk of narcolepsy observed also among adults vaccinated with Pandemrix in Finland
23 May 2013
Adults aged less than 65 years who had received Pandemrix-vaccine in 2009 and 2010 to protect against the pandemic influenza A(H1N1) had an increased risk of developing narcolepsy during the first months following vaccination compared to those unvaccinated in the same age group. According to the most recent investigation conducted by the National Institute for Health and Welfare (THL), the vast majority of adults who fell ill with narcolepsy during 2009-11 were under 40 years of age. The risk of falling ill with narcolepsy following vaccination had returned to pre-vaccination levels by eight months after the vaccination.
In Finland during 2009–11, altogether 25 adults developed narcolepsy, with 23 of the patients under 40 years of age and none older than 64 years of age. Pandemrix vaccine had been received by 18 of the confirmed narcolepsy patients. Vaccination coverage in this age group was 50 per cent. Depending on the assumptions used in the analysis, the risk of developing narcolepsy in Pandemrix-vaccinated adults aged between 20 and 64 years of age was 3–5-fold compared to non-vaccinated persons of the same age. The increased risk of narcolepsy attributed to vaccination with Pandemrix in adults was 1/100 000, whereas in children it was 6/100 000. These numbers are based on nationwide records from hospital and primary care registers, followed by an audit of the accuracy of diagnoses by neurologists and a panel of experts using individual medical records.
Increase in adult narcolepsy following vaccination previously reported in Sweden and France
A French study published in September 2012 was the first to report an increase in adult narcolepsy following Pandemrix-vaccination. However, the French study report was preliminary and therefore the results have been interpreted with caution. In March 2013, Swedish medical authorities published a registry-based study that reported a two-fold increase in young adults following Pandemrix-vaccination. In contrast to the study reported in Sweden, both the diagnoses and the vaccination records collected from the registers were validated in the THL investigation. The risk in adults has also been studied in a collaborative European-wide case-control study in the Netherlands, Italy, Norway, the UK and Denmark, but so far no increase has been observed in these countries.
Adult narcolepsy investigation more laborious than in children and adolescents
In August 2011, The National Narcolepsy Task Force reported an increased risk of narcolepsy in vaccinated children and adolescents in Finland. By that time, no increased risk in vaccinated adults was observed. Recent surveillance data have now revealed that the accumulation of records to medical registers has taken longer in adults than in children. In addition, both the verification of narcolepsy cases and vaccination data have been considerably more difficult in adults than in children.
More research is needed
THL will continue to study the association between narcolepsy and Pandemrix. The specific aim in the coming years is to verify whether vaccinated persons sought treatment sooner, which may mean that the elevated risk in the vaccinated is lower than the one reported now. In addition, continued surveillance will help to define more accurately the time interval post-vaccination which is associated with an elevated risk of narcolepsy. However, it is unlikely that future surveillance data will alter the conclusion made in this report that Pandemrix-vaccinated adults also had an increased risk of developing narcolepsy during the first months following vaccination.
Pandemrix vaccine prevented infections and fatalities caused by swine-flu virus
The Pandemrix vaccine was used to prevent a swine-flu epidemic in the winter of 2009–2010. Approximately half of the Finnish population were vaccinated. Based on register surveillance, vaccine prevented 80 000 swine flu infections, as well as approximately 50 deaths caused by swine flu virus during the first year following the vaccination.
During the winter season 2012–2013, swine flu was still the most common influenza virus causing disease in Finland, which resulted in 14 fatalities. Most recent influenza surveillance data combined with vaccination data suggest that Pandemrix vaccination during the pandemic period 2009-2010 continue to provide more than 50 per cent protection against the swine flu infection.
Jukka Jokinen, Hanna Nohynek, Jarno Honkanen, Outi Vaarala, Markku Partinen, Christer Hublin, Terhi Kilpi. Pandemiarokotteen ja narkolepsian yhteys aikuisilla. Varmennettuihin rekisteritietoihin perustuva kohorttitutkimus. Terveyden ja hyvinvoinnin laitos. Työpaperi 17/2013.
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