Background: The Vaccine Adverse Event Reporting System (VAERS) is a passive reporting system, used for monitoring the safety of all US licensed vaccines. In March 2008, ACAM2000(®) replaced Dryvax(®) as the only licensed smallpox vaccine and is administered to all persons entering military service and certain civilian researchers. In 2011, routine data mining of VAERS identified a vaccine safety concern resulting in acute ischemic cardiac events (ICE) following ACAM2000(®).

Methods: During March 1, 2008 through June 30, 2013, we reviewed all serious reports received following ACAM2000(®)and classified them by diagnostic category. We identified possible ICE cases by searching the Medical Dictionary for Regulatory Affairs (MedDRA(®)) terms for "myocardial ischaemia," "acute myocardial infarction," "myocardial infarction," and "ischaemia," and applied standardized surveillance case definitions.

Results: VAERS received 1149 reports following ACAM2000(®) administration; 169 (14.7%) were serious (resulting in permanent disability, hospitalization or prolongation of hospitalization, life-threatening illness or death), including one death. The two most frequent diagnostic categories for serious reports were cardiovascular and other infectious conditions. The MedDRA(®) search found 31 reports of possible ICE after receipt of ACAM2000(®) vaccine. Of a total 30 possible ICE cases with demographic information, all but one was male; the age range was 20-45 years (median 32) and median interval to onset of symptoms was 12 days. On clinical review there were 16 cases of myocarditis/pericarditis and 15 ICE cases.

Conclusions: Our review of the data mining signal did not substantiate the concerns about ICE after ACAM2000(®). Our study also suggests that with current pre-vaccination screening, cardiac morbidity in generally healthy vaccinated populations remains uncommon.