title: Safety of influenza vaccination in patients with myasthenia gravis: a population-based study.
abstract: Influenza vaccination has been associated with adverse events including Guillain-Barré syndrome. Because the safety of influenza vaccination in patients with myasthenia gravis (MG) has not been established, some clinicians discourage vaccination for these patients. We explored whether the administration of influenza vaccine to patients with MG might increase the risk of myasthenic crisis. Using population-based healthcare data from Ontario, Canada, from 1992 to 2007, we utilized the self-matched, case-series method of detecting adverse events following vaccination. We studied patients with established myasthenia who were hospitalized for MG within 42 weeks of influenza vaccination. We defined the primary risk interval as the 6 weeks following vaccination. Between January 1, 1992 and March 31, 2006, we identified 3667 hospital admissions for MG. No seasonal trend in MG admissions was evident. In 513 instances, hospitalization occurred within 42 weeks following vaccination in patients previously diagnosed with MG. Among these patients, 266 (52%) were men, the median age was 74 years, and 86 (17%) had previously undergone thymectomy. The estimated relative incidence of admission for MG in the primary risk interval compared with the control interval was 0.84 (95% confidence interval 0.65-1.09). We found similar results in stratified analyses according to gender, age, and thymectomy status. Vaccination of patients with MG against influenza was not found to be associated with exacerbations of the disease. Our findings do not support the practice of withholding influenza vaccination in patients with MG.
authors.affiliation: Department of Medicine, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario M4N 3M5, Canada.
authors.forename: Lorne
authors.initials: L
authors.lastname: Zinman
authors.forename: Jessica
authors.initials: J
authors.lastname: Thoma
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Kwong
authors.forename: Alex
authors.initials: A
authors.lastname: Kopp
authors.forename: Thérèse A
authors.initials: TA
authors.lastname: Stukel
authors.forename: David N
authors.initials: DN
authors.lastname: Juurlink
mesh_terms: D000328:Adult; D000368:Aged; D018450:Disease Progression; D005260:Female; D020275:Guillain-Barre Syndrome / Q000209:etiology; D006760:Hospitalization; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D009157:Myasthenia Gravis / Q000276:immunology* / Q000473:pathology; D014611:Vaccination / Q000009:adverse effects
chemical_list: D007252:Influenza Vaccines