Abstract
In 2011, the Irish Medicines Board received reports of onset of narcolepsy following vaccination against influenza A(H1N1)pdm09 with Pandemrix. A national steering committee was convened to examine the association between narcolepsy and pandemic vaccination. We conducted a retrospective population-based cohort study. Narcolepsy cases with onset from 1 April 2009 to 31 December 2010 were identified through active case finding. Narcolepsy history was gathered from medical records. Pandemic vaccination status was obtained from vaccination databases. Two independent experts classified cases using the Brighton case definition. Date of onset was defined as date of first healthcare contact for narcolepsy symptoms. Incidence of narcolepsy in vaccinated and non-vaccinated individuals was compared. Of 32 narcolepsy cases identified, 28 occurred in children/adolescents and for 24 first healthcare contact was between April 2009 and December 2010. Narcolepsy incidence was 5.7 (95% confidence interval (CI): 3.4–8.9) per 100,000 children/adolescents vaccinated with Pandemrix and 0.4 (95% CI: 0.1–1.0) per 100,000 unvaccinated children/adolescents (relative risk: 13.9; absolute attributable risk: 5.3 cases per 100,000 vaccinated children/adolescents). This study confirms the crude association between Pandemrix vaccination and narcolepsy as observed in Finland and Sweden. The vaccine is no longer in use in Ireland. Further studies are needed to explore the immunogenetic mechanism of narcolepsy.
Highlights
Narcolepsy is a sleep disorder characterised by excessive daytime sleepiness (EDS) and is often associated with cataplexy triggered by emotion such as laughter or anger
Pandemic vaccination data According to the Primary care reimbursement service (PCRS) and Pandemic data management system (PDMS) databases, 946,795 individuals received a first dose of Pandemrix between 12 October 2009 and 31 December 2010, a total of 88% of all first doses applied of pandemic vaccine
An Irish study conducted in 2009 estimated the prevalence of narcolepsy at five per 100,000 population
Summary
Narcolepsy is a sleep disorder characterised by excessive daytime sleepiness (EDS) and is often associated with cataplexy (episodic muscle weakness) triggered by emotion such as laughter or anger. Patients with narcolepsy-cataplexy carry the allele DQB1*0602 in 85–95% of cases, compared with about 30% of the general population [2]. Narcolepsy results from a decrease in levels of the neuropeptides hypocretin-1 and -2. This loss is caused by destruction of the hypocretin-producing cells in the hypothalamus region in the brain. Narcolepsy diagnosis can be confirmed by hypocretin-1 (orexin-A) measurement in the cerebrospinal fluid (CSF). This test has a high sensitivity and specificity in patients with typical cataplexy [3]. The test of reference is the multiple sleep latency test (MSLT)
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