Smallpox Vaccine-Related Myopericarditis and Encephalomyelitis Cases Under Investigation

Saturday, May 24th 2003

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Among 36,217 civilian healthcare and public health workers in the U.S. who were vaccinated against smallpox between January 24 and May 9, six "probable" and 18 "suspected" cases of myopericarditis have been reported to the Centers for Disease Control and Prevention.

One case was reported in the most recent reporting period, May 3-9, according to an update on adverse events following smallpox vaccination reported in the May 23rd issue of the Morbidity and Mortality Weekly Report.

Noting that diagnosing myopericarditis can be difficult, the CDC, in collaboration with the Smallpox Vaccine Safety Working Group of the Advisory Committee on Immunization Practices, has developed a case definition for myopericarditis, which they have yet to release but will be published in an upcoming issue of the MMWR.

The CDC is also investigating one case of suspected postvaccinial encephalomyelitis (PVE) reported during the first week of May.

PVE is a "rare" adverse event associated with smallpox immunization, they note in MMWR, and several features of this case are atypical of PVE. In addition, there are other potential causes for the occurrence of PVE in this patient, investigators note.

"Temporal association with vaccination does not necessarily indicate causality," according to the CDC report. "In the setting of smallpox vaccination, patients with acute mental status changes, focal neurologic deficits or white matter lesions on MRI must be evaluated for other more common causes of encephalomyelitis and treatable etiologies such as herpes simplex encephalitis should be excluded," they write.

Nonetheless, the CDC encourages state health departments to promptly report neurologic adverse events following smallpox vaccination.

During May 3-9, one other "serious" adverse event--a patient who required hospitalization and antibiotic administration--and 23 "nonserious" events were reported. No cases of vaccinia transmission occurred.

The most common side effects continue to be rash, fever, headache, pruritus, fatigue, and pain, "consistent with mild expected reactions following receipt of smallpox vaccine," CDC officials add.

Source
MMWR 2003;52:475-477
May 22 2003

 

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