Narcolepsy and swine flu vaccine

There have been several reports to suggest that the swine flu vaccine may cause narcolepsy in rare cases, due to its stimulating effect on antibodies that disable sleep-regulating brain cells.

Narcolepsy

Narcolepsy is a chronic disorder of the central nervous system that affects the ability of brain cells to regulate sleep cycles as normal.

A large number of neurons in the hypothalamus are usually responsible for producing the orexin hormone, also known as hypocretin, that helps to make individuals feel awake. These neurons are destroyed or disabled in patients with narcolepsy, causing them to fall asleep more frequently than usual. Management of the condition currently involves a combination of medications to aid sleep at night and stimulants to maintain wakefulness during the day.

The pathogenesis of the disorder and the cause of the neuronal destruction are highly variable, but it is believed to be an autoimmune response. The antibodies responsible for this may be triggered by certain infections, including influenza.

Swine Flu Vaccine

The swine flu vaccine, Pandemrix by GlaxoSmithKline, is believed to trigger an immune response that may cause the onset of narcolepsy in rare cases.

This reaction likely occurs due to the similarity of the H1N1 proteins and the neurons in the hypothalamus that produce the orexin hormone. This leads to the immune reaction that destroys the brain cells that have an effect on sleep regulation.

For affected patients, symptoms of narcolepsy typically presented within a few months following vaccination with Pandemrix. However, it is worth noting that since the initial findings individuals that have been vaccinated have received greater attention in this area and may have received an earlier diagnosis of narcolepsy from other causes as a result.

Epidemiological Association

The association between narcolepsy and the swine flu vaccine has been observed in epidemiological data, which noted a rise in the incidence of narcolepsy in countries that utilized Pandemrix to prevent swine flu during the pandemic.

It is estimated that every 55,000 vaccinations result in one case of narcolepsy attributable to the vaccine, compared to the general population. However, there are various other possible causes of the condition, and it is not possible to declare with certainty that Pandemrix can take full responsibility for the epidemiological observations.

Mechanism of Action and Research

Although there were several different swine flu vaccines used during the pandemic, Pandemrix exhibited a stronger association with narcolepsy than other brands, such as Focetria by Novartis.

Both vaccines contain a protein that is similar in structure to the orexin receptor, but Pandemrix had a higher concentration of the protein than Focetra. As a result, it was hypothesized that this protein induced an autoimmune response that destroyed the orexin cells in the brain and caused narcolepsy.

This effect was tested in individuals that had received the Pandemrix vaccine and supported by the results, which showed that 85% of them had elevated levels of antibodies that target the receptor. Accordingly, none of the control group that received the Focetria vaccine exhibited elevated levels of the antibodies.

There have been studies observing the effect of the swine flu vaccine used in various countries worldwide, with a similar effect evident. This remains true for various age groups, from young children to adults that have received the Pandemrix swine flu vaccination.

References

• http://www.ncbi.nlm.nih.gov/pubmed/25320099
• http://www.bmj.com/content/346/bmj.f794#aff-3
• https://med.stanford.edu/news/all-news/2015/07/side-effect-of-flu-vaccine-yields-new-insights-into-narcolepsy.html
• http://stm.sciencemag.org/lookup/doi/10.1126/scitranslmed.aab2354