According to the review, the Department of Defense Smallpox Vaccination Program reported over 50 cases to date of myopericarditis - inflammation of the heart muscle or of the sac surrounding the heart - following vaccination.
"Reported rates of non-cardiac complications have been very low, in line with the rates of complications we saw historically, when children were routinely vaccinated for smallpox," said Dimitri C. Cassimatis, M.D., first author of the review and cardiology fellow at Walter Reed Army Medical Center in Washington, D.C. "The rate of cardiac complications, however, has been higher than expected."
"The individuals experiencing complications have responded well to therapy and almost all revert to normal," said Dr. Cassimatis. "More serious cardiac events, such as heart attacks and arrhythmias have not occurred at a rate greater than you would expect in this size population.
The U.S. Department of Defense resumed smallpox vaccination of military personnel in December 2002. As of June 2003, more than 450,000 military personnel have been vaccinated and carefully followed to identify and manage any adverse reactions to the vaccine. The Vaccine Health Care Center has systems in place to monitor and keep records of any adverse side effects resulting from any vaccination, including smallpox, according to Dr. Cassimatis.
"The rates of non-cardiac side effects, most of them quite mild, were at or below historic rates," he said. "The rate of myopericarditis was approximately eight out of 100,000 in those who received the vaccine for the first time - a rate similar to what had been reported in some European literature of the 1960s and 1970s," said Dr. Cassimatis. "This cardiac side effect was virtually unreported in the U.S. experience with vaccination. Fortunately, Dr. Renata Engler, who spearheaded the creation of the Vaccine Health Care Center and is the chief of allergy and immunology here at Walter Reed, was familiar with the European literature and alerted us to the possibility of myopericarditis. As a result we were ready to monitor and treat anyone who developed this problem."
Dr. Cassimitis said future research is needed to better quantify the risk of myopericarditis after smallpox vaccination.
"While the total number affected remains relatively small, we must recognize that the administration of smallpox vaccinations has been limited. The numbers could rise significantly if a more widespread civilian vaccination program was implemented. We need to better understand the potential complications with this small group so we are adequately prepared to address complications on a larger scale if that ever becomes necessary."
Media Advisory: To contact Dimitri C. Cassimatis, M.D., call the Walter Reed Public Affairs Office at 202-782-7177. On the day of the briefing, call the AMA's Science News Department at 312-464-2410.