Registry Cohort Study to Determine Risk for Multiple Sclerosis after Vaccination for Pandemic Influenza A(H1N1) with Arepanrix, Manitoba, Canada

To investigate a potential risk for multiple sclerosis (MS) after vaccination with Arepanrix, the GlaxoSmithKline AS03adjuvanted influenza A(H1N1)pdm09 vaccine, we used the provincewide immunization registry for Manitoba, Canada, to match 341,347 persons vaccinated during the 2009 pandemic to 485,941 unvaccinated persons on age, sex, address, and a propensity score measuring the probability of vaccination.We used a previously validated algorithm to identify MS cases from provincial hospital, physician, and prescription drug claims databases.After 12 months of follow-up, the age-adjusted incidence rate of MS was 17.7 cases per 100,000 person-years in the Arepanrix cohort and 24.2 per 100,000 in the unvaccinated cohort.The corresponding adjusted hazard ratio was 0.9.We observed similar patterns when we measured incidence over the entire follow-up period.The AS03 adjuvant, a candidate for inclusion in future pandemic vaccines, does not appear to increase the short-term risk for MS when included in influenza vaccines. M ultiple sclerosis (MS) is a chronic debilitating diseaseof the central nervous system (CNS) that affects >2.5 million persons worldwide (1).Its etiology is unknown but most likely is due to complex interactions between genetic and environmental factors (2).A role for infectious agents and vaccines has been suggested (2), but concrete evidence is lacking (3-6).Soon after the 2009 influenza A(H1N1) pandemic, a signal of increased incidence of MS was detected in a postlicensure record-linkage study among residents of 3 counties in Sweden who received Pandemrix (GlaxoSmithKline, Dresden, Germany), an inactivated monovalent AS03-adjuvanted influenza A(H1N1)pdm09 vaccine (7).Another study from Stockholm, Sweden, reported increased risk for paraesthesias, but not of MS, among persons vaccinated with Pandemrix (8).Neither study was designed to assess an association with MS, and neither used validated algorithms for identifying MS from administrative databases.Because AS03, an adjuvant system containing α-tocopherol and squalene in an oil-in-water emulsion ( 9), is likely to be used in future pandemic vaccines, the European Medicine Agency mandated a study to evaluate the relationship between use of the GlaxoSmith-Kline AS03-adjuvanted pandemic vaccines and MS.We assessed whether use of another AS03-adjuvanted A(H1N1)pdm09 vaccine, Arepanrix (GlaxoSmithKline, Quebec City, QC, Canada), was associated with increased risk for incident MS in Manitoba, Canada.Because of a combination of genetic and environmental factors, the prevalence of MS varies geographically (2).Canada is a high-prevalence region for MS.Within Canada, the prevalence of MS is particularly high in central and western provinces, such as Manitoba (10,11).Our secondary objective was to assess whether administration of Arepanrix was associated with increased risk for CNS demyelinating events that do not ultimately lead to MS (hereafter other demyelinating conditions). Methods Design and Data SourcesManitoba Health is a government agency that provides publicly funded universal healthcare to virtually all of Manitoba's 1.3 million residents.Insured services include hospital, physician, and preventive services, including vaccinations.All provided services are recorded in centralized electronic databases that can be linked using a unique lifetime personal health identification number (PHIN).A population registry tracks addresses and dates of birth, Registry Cohort Study to Determine Risk for Multiple Sclerosis after Vaccination for Pandemic Influenza A(H1N1) withArepanrix, Manitoba, Canada

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