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Institute for Vaccine Safety

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Update on Smallpox Adverse Events


The US Department of Defense's website reports on serious adverse events among military personnel. In the 18 months between 13 Dec 02 and 13 Jun 04, the DoD administered 627,499 smallpox vaccinations.

The CDC website on smallpox vaccine safety  also provides a link to a series of MMWR articles covering the adverse events reported to date and comments regarding possible or probably causal relationships.


Enterovirus: any of a genus (Enterovirus) of picornaviruses (as the causative agent of poliomyelitis) that typically occur in the gastrointestinal tract but may be involved in respiratory ailments, meningitis, and neurological disorders.

Infarction: an area of necrosis in a tissue or organ resulting from obstruction of the local circulation by a thrombus or embolus

Myocardidits:  an inflammation of the heart muscle.

Myocardial infarction: infarction of the myocardium that results typically from coronary occlusion, that may be marked by sudden chest pain, shortness of breath, nausea, and loss of consciousness, and that sometimes results in death

Myopericarditis: inflammation of both the myocardium and pericardium.

Pericarditis: a disorder caused by inflammation (swelling and irritation with presence of extra immune cells) of the pericardium, which is the sac-like covering of the heart.

source:  Merriam Webster/MedLine

Adverse Events

The most interesting developments in the experience to date are the cases of myocarditis or pericarditis (sometimes termed myopericarditis). There is a clustering in time for onset of this disorder with the peak occurring 7-12 days after vaccination similar to the peak in other adverse events associated with viral replication. This disorder has occurred during the winter and early spring which is the off-season for enterovirus disease, another cause of infectious myocarditis. Although a definitive answer has not been provided, many experts believe that this disorder will be linked causally to the vaccine. To date, all affected individuals appear to have recovered but long-term follow-up is necessary to determine the outcome. There have also been cases of ischemic heart disease including fatal myocardial infarctions in both the military and civilian populations. At this time, the incidence of those disorders appears to be similar to what might be expected although further analyses are in place. There is a less clear evidence of any time clustering and it is possible that these may be coincidental.

There have been instances of both autoinoculation of separate body sites and transmission to close contacts in both the military and civilian population emphasizing the need for careful screening of vaccinees to avoid vaccinating individuals who are in close contact with persons who have a contraindication to vaccination.

IOM Reviews - Smallpox Vaccination Program Implementation

Review of the Centers for Disease Control and Prevention’s Smallpox Vaccination Program Implementation: Letter Report #6 [7-6-04] available to read online.

For information on SVPI meetings and related reports click here.

This page was last updated on August 08, 2012

Institute for Vaccine Safety