Smallpox Vaccination-Associated Myopericarditis

Dryvax, a freeze-dried calf lymph smallpox vaccine was used extensively from the 1940s to the 1980s but was replaced in 2008 by ACAM2000, a smallpox vaccine cultured in kidney epithelial cells from African green monkeys.^3,5 Myopericarditis was rarely associated with the Dryvax, with only 5 cases reported from 1955 to 1986 after millions of doses of vaccines were administered; however, in 230,734 administered ACAM2000 doses, 18 cases of myopericarditis (incidence, 7.8 per 100,000) were reported during a surveillance study in 2002 and 2003.^3,5

Myopericarditis presents with a wide variety of symptoms, such as chest pain, palpitations, chills, shortness of breath, and fever.^6,7 Mainstay diagnostic criteria include ECG findings consistent with myopericarditis (such as diffuse ST segment elevations) and elevated cardiac biomarkers (elevated troponins).^5-7 An echocardiogram can be helpful in diagnosis, as most cases will not have regional wall motion abnormalities (to distinguish against coronary artery disease).^5-7 MRI with diffuse enhancement of the myocardium can be helpful in diagnosis.^5,6 The gold standard for diagnosis is an endomyocardial biopsy, which carries a significant risk of complications and is not routinely performed to diagnose myopericarditis.^5,6 US military smallpox vaccination data showed that the onset of vaccine-associated myopericarditis averaged (SD) 10.4 (3.6) days after vaccination.⁵

Vaccine-associated myopericarditis treatment is focused on decreasing inflammation.^5,6 Nonsteroidal anti-inflammatory drugs are advised for about 2 weeks with cessation of intensive cardiac activities for between 4 and 6 weeks due to risks of congestive heart failure and fatal cardiac arrhythmias.^5,6

Conclusions

Since the September 11 attacks, the US needs to be continually prepared for potential terrorism on American soil and abroad. The threat of bioterrorism has renewed efforts to vaccinate or revaccinate American service members deployed to high-risk regions. These vaccinations put them at risk for vaccination-induced complications that can range from mild fever to life-threatening complications.