title: Acute Demyelinating Events Following Vaccines: A Case-Centered Analysis.
abstract: BACKGROUND
  Case reports have suggested that vaccines may trigger transverse myelitis (TM) or acute disseminated encephalomyelitis (ADEM), but the evidence for a causal association is inconclusive. We analyzed the association of immunization and subsequent development of TM or ADEM.
  
  
  METHODS
  We identified all cases of TM and ADEM in the Vaccine Safety Datalink population. Using a case-centered method, we compared vaccination of each case to vaccination of all matched persons in the study population, who received the same type of vaccine, with respect to whether or not their vaccination occurred during a predetermined exposure interval. We calculated a risk difference (excess risk) of TM and ADEM for each vaccine.
  
  
  RESULTS
  Following nearly 64 million vaccine doses, only 7 cases of TM and 8 cases of ADEM were vaccinated during the primary exposure window 5-28 days prior to onset. For TM, there was no statistically significant increased risk of immunization. For ADEM, there was no statistically significant increased risk following any vaccine except for Tdap (adolescent and adult tetanus, reduced diphtheria, acellular pertussis) vaccine. Based on 2 exposed cases, the odds ratio for Tdap exposure 5-28 days prior to ADEM onset was 15.8 (95% confidence interval [CI], 1.2-471.6; P = .04), and the estimated excess risk was 0.385 (95% CI, -.04 to 1.16) cases per million doses.
  
  
  CONCLUSIONS
  We found no association between TM and prior immunization. There was a possible association of ADEM with Tdap vaccine, but the excess risk is not likely to be more than 1.16 cases of ADEM per million vaccines administered.
authors: Northern California Kaiser Permanente Vaccine Study Center, Oakland.
authors: Roger
authors: R
authors: Baxter
authors: Northern California Kaiser Permanente Vaccine Study Center, Oakland.
authors: Edwin
authors: E
authors: Lewis
authors: Northern California Kaiser Permanente Vaccine Study Center, Oakland.
authors: Kristin
authors: K
authors: Goddard
authors: Northern California Kaiser Permanente Vaccine Study Center, Oakland.
authors: Bruce
authors: B
authors: Fireman
authors: Permanente Medical Group, Antioch, California.
authors: Nandini
authors: N
authors: Bakshi
authors: Immunization Safety Office, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors: Frank
authors: F
authors: DeStefano
authors: Immunization Safety Office, Centers for Disease Control and Prevention, Atlanta, Georgia.
authors: Julianne
authors: J
authors: Gee
authors: Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena.
authors: Hung Fu
authors: HF
authors: Tseng
authors: Center for Health Research, Kaiser Permanente Northwest, Portland, Oregon.
authors: Allison L
authors: AL
authors: Naleway
authors: Northern California Kaiser Permanente Vaccine Study Center, Oakland.
authors: Nicola P
authors: NP
authors: Klein
mesh_terms: D000293:Adolescent; D000328:Adult; D019433:Chickenpox Vaccine / Q000009:adverse effects; D002648:Child; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage / Q000009:adverse effects; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000009:adverse effects; D004673:Encephalomyelitis, Acute Disseminated / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D006801:Humans; D007115:Immunization Schedule; D007252:Influenza Vaccines / Q000009:adverse effects; D008297:Male; D009188:Myelitis, Transverse / Q000453:epidemiology / Q000209:etiology*; D012306:Risk; D014611:Vaccination; D014612:Vaccines / Q000008:administration & dosage / Q000009:adverse effects*
chemical_list: D019433:Chickenpox Vaccine; D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines; D007252:Influenza Vaccines; D014612:Vaccines
keywords: acute disseminated encephalomyelitis; immunization; transverse myelitis; vaccine