Rigorous smallpox vaccine safety screening, educational programs, and older vaccinees may have contributed to low rates of preventable life-threatening adverse reactions. Other rare, clinically significant, or unexpected cardiac adverse events were detected by timely review of VAERS data and intensive clinical case investigation.

Myocarditis was reported after smallpox vaccination in Europe and Australia, but no association had been reported with the US vaccine. We conducted surveillance to describe and determine the frequency of myocarditis and/or pericarditis (myo/pericarditis) among civilians vaccinated during the US smallpox vaccination program between January and October 2003. We developed surveillance case definitions for myocarditis, pericarditis, and dilated cardiomyopathy after smallpox vaccination. We identified 21 myo/pericarditis cases among 37,901 vaccinees (5.5 per 10,000); 18 (86%) were revacinees, 14 (67%) were women, and the median age was 48 years (range, 25-70 years). The median time from vaccination to onset of symptoms was 11 days (range, 2-42 days). Myo/pericarditis severity was mild, with no fatalities, although 9 patients (43%) were hospitalized. Three additional vaccinees were found to have dilated cardiomyopathy, recognized within 3 months after vaccination. We describe an association between smallpox vaccination, using the US vaccinia strain, and myo/pericarditis among civilians.

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Generalized vaccinia (GV), progressive vaccinia (PV), and eczema vaccinatum (EV) are adverse reactions following smallpox vaccination. We investigated all reports suggestive of GV, PV, or EV among United States civilian smallpox vaccinees during 2003 and applied standard case definitions. We identified 29 reports of possible GV among 38,440 vaccinees; 2 (7%) of the reports met the case definition. One case of GV was confirmed by identifying vaccinia from a lesion distant from the vaccine site using polymerase chain reaction. The other case was classified as probable GV, because confirmatory testing was not done. We identified 3 potential EV cases and 7 potential PV cases, none of which met the standard case definition. GV, PV, and EV were rare or absent following smallpox vaccination after careful screening of potential vaccinees. GV may be difficult to distinguish from other rashes, and confirmatory testing is recommended. Careful prevaccination screening probably contributed to the low incidence of these adverse reactions following smallpox vaccination.