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Research findings
New study:

Narcolepsy after swine influenza pandemic

A new Norwegian study confirms that the risk of narcolepsy was increased after vaccination with Pandemrix during the influenza pandemic in 2009/2010. It also suggests that the risk of narcolepsy increased after influenza, but these figures must be interpreted with caution.

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“We studied the relationship between vaccination with Pandemrix and the development of narcolepsy among 1.6 million children and young people under the age of 30 in Norway. In addition, we looked at the association between influenza and narcolepsy,” says Dr Lill Trogstad from the Norwegian Institute of Public Health. 

Almost 700,000 people in this age group (41.9 per cent) were vaccinated and just under 60,000 (3.6 per cent) were diagnosed with influenza by a doctor during the pandemic. The majority of people who became ill during the pandemic did not seek medical advice. However, studies in Norway, have estimated that about 30 per cent of the population were infected.

From October 2009, when the pandemic began, until the end of 2012, narcolepsy was confirmed in 72 patients aged 5-26 years. The average age at onset was 12 years. 56 of the patients were vaccinated and 16 were unvaccinated. This shows that unvaccinated individuals were also at risk of developing narcolepsy. The average time from vaccination until the development of narcolepsy symptoms was 8 months.

The overall incidence of narcolepsy in this period was 1.40 per 100,000 individuals per year. This means that when following 100,000 individuals for one year, one or two new cases of the disease were diagnosed. Fortunately, narcolepsy is a rare disease, but it has serious implications for those affected.

“The association between vaccination and narcolepsy was strong, as we expected. After a 3-year follow-up, the risk of narcolepsy was about five times higher for vaccinated individuals than for those who were unvaccinated. This relationship is well-known from before and is confirmed in our study,” says Trogstad.

The data also showed that children and young people were mainly vaccinated after the influenza pandemic had peaked. Consequently, many of those who were vaccinated may also have had influenza.

“The limited information about influenza in our study gives great uncertainty in the calculations of risk for such a rare disease like narcolepsy. However, there was a slight, statistically significant association between influenza and an increased risk of narcolepsy during the first six months after infection. Also, it cannot be ruled out that having influenza at the same time as vaccination may increase the risk of narcolepsy, but we cannot conclude this from our data” emphasises Trogstad.

The risk of narcolepsy after influenza is generally poorly studied, but an increased incidence of narcolepsy after the influenza pandemic was also seen in countries with low levels of vaccination, including China and Denmark.

Pandemic research at the NIPH

Norway has excellent national health registries. These make it possible to measure the impact of the swine influenza pandemic on the population’s health on a scientific basis, both in terms of the effect of vaccination and influenza. This is the fifth registry-based study published by the Norwegian Institute of Public Health as part of the research-based surveillance of the swine influenza pandemic in 2009/10.

The previous studies have examined the impact of influenza and vaccination with Pandemrix on pregnancy outcomes, chronic fatigue syndrome, Guillain-Barre syndrome and febrile seizures in children.

The other studies have shown that:

  • Vaccination with Pandemrix reduced the risk of influenza illness by about 70 per cent.
  • Influenza in pregnancy was associated with a nearly doubled risk of stillbirth.
  • There was no increased risk of stillbirth after vaccination with Pandemrix.
  • Influenza illness was associated with a doubled risk for chronic fatigue syndrome.
  • There was no increased risk of chronic fatigue syndrome in the population following vaccination with Pandemrix.
  • In children under four years with influenza, the risk of febrile seizures was 116 times higher than in children without influenza.
  • In children under four years, the risk of febrile seizures was twice as high 1-3 days after vaccination compared with children who were not vaccinated.
  • Influenza illness was associated with an almost five-fold risk of Guillain-Barre syndrome.
  • The risk of Guillain-Barré syndrome in the population was not increased after vaccination with Pandemrix.

 

References

  1. Håberg SE, Trogstad L, Gunnes N, Wilcox AJ, Gjessing HK, Samuelsen SO et al. Risk of fetal death after pandemic influenza infection or vaccination during pregnancy. N Engl J Med (2013). DOI: 10.1056/NEJMoa1207210
  2. Magnus P, Gunnes N, Tveito K, Bakken IJ, Ghaderi S, Stoltenberg C, Hornig M, Lipkin IW, Trogstad L, Håberg S. Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is associated with pandemic influenza infection, but not with an adjuvanted pandemic influenza vaccine. Vaccine (2015), http://dx.doi.org/10.1016/j.vaccine.2015.10.018
  3. Ghaderi S, Gunnes N, Bakken IJ, Magnus P, Trogstad L, Håberg SE. Risk of Guillain-Barré syndrome after exposure to pandemic influenza A(H1N1)pdm09 vaccination or infection: a Norwegian population-based cohort study. Eur J Epidemiol DOI 10.1007/s10654-015-0047-0.
  4. Bakken IJ, Aaberg KM, Ghaderi S, Gunnes N, Trogstad L, Magnus P, Håberg SE. Febrile seizures after 2009 influenza A (H1N1) vaccination and infection: a nationwide registry-based study. BMC Infectious Diseases (2015) 15:506 DOI 10.1186/s12879-015-1263-7
  5. Trogstad L, Bakken IJ, Gunnes N, Ghaderi S, Stoltenberg C, Magnus P, Håberg SE. Narcolepsy and hypersomnia in Norwegian children and young adults following the influenza A(H1N1)2009 pandemic. Vaccine (2017), http://dx.doi.org/10.1016/j.vaccine.2017.02.053