Neurologic Adverse Events Associated With Smallpox Vaccination in the United States, 2002-2004


Journal of the American Medical Association
November 23/30, 2011, Vol 306, No. 20, pp 2187-2283

  1. James J. Sejvar, MD;
  2. Robert J. Labutta, MD;
  3. Louisa E. Chapman, MD, MPH;
  4. John D. Grabenstein, PhD, RPh;
  5. John Iskander, MD, MPH;
  6. J. Michael Lane, MD, MPH

  1. Author Affiliations: Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases (Dr Sejvar) and Epidemiology and Surveillance Division, National Immunization Program (Drs Chapman and Iskander), Centers for Disease Control and Prevention, Atlanta, Ga; Department of Neurology, Walter Reed Army Medical Center, Washington, DC (Dr Labutta); and Military Vaccine Agency, United States Army Medical Command, Falls Church, Va (Dr Grabenstein). Dr Lane is the former director of the Smallpox Eradication Program, Centers for Disease Control and Prevention.
  1. Corresponding Author: James J. Sejvar, MD, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd, Mailstop A-39, Atlanta, GA 30333 (


Context  Neurologic illness is an infrequent but severe adverse event associated with smallpox vaccination. The reinstatement of smallpox vaccination in the United States in response to possible bioterrorism renewed concerns about vaccine-related adverse neurologic events.

Objective  To determine rates and describe the clinical features of neurologic events associated with smallpox vaccination.

Design and Setting  We assessed reports of adverse events obtained through active case reporting and review of data reported to the Vaccine Adverse Event Reporting System among 665 000 persons vaccinated against smallpox by the Departments of Defense (n = 590 400) and Health and Human Services (n = 64 600) during the 2002-2004 US Smallpox Vaccination Program.

Main Outcome Measure  Adverse neurologic events temporally associated with smallpox vaccination.

Results  Between December 16, 2002, and March 11, 2004, 214 neurologic adverse events temporally associated with smallpox vaccination were reported; 111 reports involved Department of Health and Human Services and 103 involved Department of Defense vaccinees. Fifty-four percent of these events occurred within 1 week of vaccination, and 53% were among primary vaccinees. The most common neurologic adverse event was headache (95 cases), followed by nonserious limb paresthesias (n = 17) or pain (n = 13) and dizziness or vertigo (n = 13). Serious neurologic adverse events included 13 cases of suspected meningitis, 3 cases of suspected encephalitis or myelitis, 11 cases of Bell palsy, 8 seizures (including 1 death), and 3 cases of Guillain-Barré syndrome. Among these 39 events, 27 (69%) occurred in primary vaccinees and all but 2 occurred within 12 days of vaccination.

Conclusions  During the 2002-2004 smallpox vaccination campaign, reported neurologic events were generally mild and self-limited, and no neurologic syndrome was identified at a rate above baseline estimates. Serious neurologic adverse events, such as postvaccinal encephalitis, Bell palsy, and Guillain-Barré syndrome, occurred in accordance with expected ranges.

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