How was the Pandemrix vaccine linked to narcolepsy cases in some countries?

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Caring for flu victims — influenza pandemic (H1N1) of 2009 Doctors at the Mexico City Navy Hospital wearing protective gear as they tend to patients complaining of H1N1 flu-like symptoms.

Following the 2009 H1N1 pandemic, the Pandemrix vaccine, developed by GlaxoSmithKline, was linked to an increased incidence of narcolepsy, a sleep disorder characterized by sudden, uncontrollable sleep spells.1

In 2011, investigations revealed a significant correlation between the vaccine and the disorder, particularly among younger populations. For instance, in Finland, individuals aged 4 to 19 who received the vaccine faced a risk of narcolepsy nine times higher than their unvaccinated peers. Research indicated that the vaccine increased this risk primarily in individuals who already possessed a specific genetic variation that predisposed them to the condition.1

While similar outbreaks were investigated in 11 other countries, health officials emphasized that the overall benefits of H1N1 vaccination continued to outweigh the risks of potential side effects.1