Risk of Narcolepsy Associated With Administration of Inactivated Adjuvanted (AS03) A/H1N1 Pandemic Influenza Vaccine in Quebec

This study aims to describe the epidemiological and clinical characteristics of cases of narcolepsy which occurred in Quebec during the period 1 January 2009 to December 31, 2010 and to assess the risk of developing narcolepsy associated with the vaccine against influenza A/H1N1. The study will last about six months. Based on the prevalence of narcolepsy, an estimated 100 people who developed symptoms of narcolepsy between January 1st, 2009 and December 31, 2010 will participate in this study at the sleep clinic of the Sacré-Coeur Hospital in Montreal.

Narcolepsy is primarily characterized by the presence of excessive daytime sleepiness (EDS) and cataplexy. EDS occurs daily and is usually the most disabling symptom of narcolepsy. Cataplexy consists of a sudden drop of muscle tone triggered by strong and sudden emotions such as laughter, anger and surprise. Cataplexy is the most specific symptom of narcolepsy but it is not present in every patient especially at disease onset. Two other auxiliary symptoms are sleep paralysis and hypnagogic hallucinations either at sleep onset or upon awakening during the night or in the morning. They are present in approximately two thirds of narcoleptic patients especially in the younger individuals during the early stage of narcolepsy. Narcolepsy is associated with an absence or low level of hypocretin1 peptide in the cerebrospinal fluid (CSF).

Narcolepsy with cataplexy can be diagnosed purely on clinical grounds but this diagnosis should whenever possible be confirmed by night-time polysomnography (PSG) followed by the daytime multiple sleep latency test (MSLT). Sleep latency on the MSLT should be inferior or equal to 8 minutes with the presence of two or more sleep onset REM periods (SOREMPs). Human leukocyte antigen (HLA) typing of patients with narcolepsy-cataplexy almost always shows the presence of HLA DQB1*0602. Finally, measuring CSF level of hypocretin-1 is specific and sensitive for the diagnosis of narcolepsy with cataplexy.

Cases of narcolepsy following administration of A/H1N1 pandemic vaccines have been reported in Sweden, Finland, France and Canada. The majority of reports have shown a temporal association with inactivated (AS03) adjuvanted A/H1N1 vaccines. These cases had some common features: severe sleepiness and presence of cataplexy, abrupt onset and rapid evolution, presence of HLA DBQ1*0602 marker, very low CSF hypocretin-1, and positive MSLT test. At the request of the European Medicines Agency (EMA), a series of investigations have been considered by GlaxoSmithKline Biologicals, including one in Quebec. In this province, following the report of four cases of narcolepsy with cataplexy potentially associated with administration of Arepanrix, our research team was contacted both by federal and provincial public health authorities to evaluate the possibility of an independent investigation.

A retrospective cohort study is proposed. The existence of a comprehensive influenza immunization registry in Quebec allows a precise identification of the cohort of exposed subjects, by age and gender. Exposed subjects will be followed from the time of vaccine administration (first dose of inactivated AS03 A/H1N1 pandemic vaccine) as recorded in the immunization registry. The size of non-exposed subjects by gender- and age-specific categories will be estimated from the number in census data (a more accurate source than provincial health insurance data) minus the number in the influenza immunization registry. Pseudo-dates of vaccine administration will be generated for non-exposed subjects based on the distribution of dates of vaccinated subjects. Non-exposed subjects will be followed from the pseudo-date of vaccine administration.