Since December 2002, roughly 500,000 civilian health care workers and military personnel in the United States have been immunized against smallpox. According to federal health officials, the rate of serious side effects has been surprisingly low due to stringent rules designed to prevent smallpox vaccination among people at high risk for complications; however, a serious complication has arisen in the form of inflammation of the heart tissue. Nevertheless, predictions from government experts suggested that there would be between 14 and 52 life-threatening reactions and one or two deaths for every 1 million people vaccinated, based on 1960s figures, but the 454,856 military personnel immunized in the past seven months have shown just 32 mild skin rashes and one case of encephalitis, though that was not conclusively associated with the smallpox vaccine. The heart inflammation, called myopericarditis, appears to have emerged in 46 vaccinated people in the military, with 22 suspected or probable cases among health care workers.