Narcolepsy and 2009 H1N1 pandemic vaccination in Taiwan.

Background: Several European countries have observed an association between narcolepsy and H1N1 vaccines containing AS03® adjuvant in children/adolescents. In Taiwan, a nationwide campaign starting November 2009 administered H1N1 vaccines without adjuvant or with MF59® adjuvant to 67% of children and 12% of adults.

Methods: For those registered in the 2000-2012 National Health Insurance (NHI) databases, we compared age-stratified (0-4, 5-18, 19-59, and ≥60 years) incidence of first referral for a diagnostic MSLT for the pre-pandemic, pandemic/pre-vaccination, and vaccination/post-pandemic period. We also compared the odds of H1N1 vaccination in each chart-ascertained narcolepsy patient, whoever had an onset of excessive daytime sleepiness between April 2009 and December 2012, with 10 population-based controls from the NHI databases on year of birth, sex, and index date, using conditional logistic regressions.

Results: Incidence of MSLT referral for narcolepsy was highest and significantly increased in the pandemic/pre-vaccination period in the age group 5-18 (IRR 3.40, 95% confidence intervals (CI) 2.12-5.45) and 19-59 (IRR 2.90, 95% CI 1.62-5.02) years. Among 137 confirmed narcolepsy cases (86 adults and 51 children), the odds ratios (ORs) were 1.67 (95% CI 0.81-3.45) (adults) and 1.22 (95% CI 0.62-2.39) (children) for H1N1 vaccination without adjuvant, and 1.39 (95% CI 0.17-11.48) (adults) and 3.66 (95% CI 0.37-36.02) (children) with MF59® adjuvant.

Conclusion: No substantial association between the use of H1N1 vaccines and narcolepsy was identified in Taiwan. Instead, the H1N1 infection itself could have played a role in triggering narcolepsy in children and young adults.