Highlights

• •In Germany, pandemic influenza vaccination coverage was low.
• •An increased risk for narcolepsy after pandemic H1N1 vaccination is supported.
• •This risk applies to children and adolescents as well as adults.
• •Exposed cases had a more severe clinical picture as compared to nonexposed cases.
• •No other risk factors for narcolepsy were identified.

Abstract
Objective
Studies associate pandemic influenza vaccination with narcolepsy. In Germany, a retrospective, multicenter, matched case–control study was performed to identify risk factors for narcolepsy, particularly regarding vaccinations (seasonal and pandemic influenza vaccination) and infections (seasonal and pandemic influenza) and to quantify the detected risks.

Methods
Patients with excessive daytime sleepiness who had been referred to a sleep center between April 2009 and December 2012 for multiple sleep latency test (MSLT) were eligible. Case report forms were validated according to the criteria for narcolepsy defined by the Brighton Collaboration (BC). Confirmed cases of narcolepsy (BC level of diagnostic certainty 1−4a) were matched with population-based controls by year of birth, gender, and place of residence. A second control group was established including patients in whom narcolepsy was definitely excluded (test-negative controls).

Results
A total of 103 validated cases of narcolepsy were matched with 264 population-based controls. The second control group included 29 test-negative controls. A significantly increased odd ratio (OR) to develop narcolepsy (crude OR [cOR] = 3.9, 95% confidence interval [CI] = 1.8–8.5; adjusted OR [aOR] = 4.5, 95% CI = 2.0–9.9) was detected in individuals immunized with pandemic influenza A/H1N1/v vaccine prior to symptoms onset as compared to nonvaccinated individuals. Using test-negative controls, in individuals immunized with pandemic influenza A/H1N1/v vaccine prior to symptoms onset, a nonsignificantly increased OR of narcolepsy was detected when compared to nonvaccinated individuals (whole study population, BC levels 1−4a: cOR = 1.9, 95% CI = 0.5–6.9; aOR = 1.8, 95% CI = 0.3–10.1).

Conclusions
The findings of this study support an increased risk for narcolepsy after immunization with pandemic influenza A/H1N1/v vaccine.