ences between the experience of developing nations and that of developed nations. The reaction rate of vaccinees in developing countries may be confounded by malnutrition, co-infections, and other factors. Furthermore, experience with smallpox vaccine in the United States was largely in infants, and adequate surveillance among adults may have been lacking. Specific events, such as the New York smallpox outbreak in 1947 provide some evidence about vaccinating adults. Four main complications may be associated with vaccination; three complications are in the form of skin eruptions (eczema vaccinatum, progressive vaccinia, and generalized vaccinia) and a fourth, and the most serious, is postvaccinial encephalitis (CIDRAP and IDSA, 2004). Two studies conducted in 1968, a national study and a 10 state study of these complications, provide somewhat different estimates of vaccine adverse event rates, reflecting differences in methods and case definitions (for example, the case definition of generalized vaccinia). In the national survey, 14 million people were vaccinated, leading to a total of 9 deaths, 11 cases of progressive vaccinia, 74 cases of eczema vaccinatum, 143 cases of generalized vaccinia, and 16 cases of encephalitis (WHO, 2001). Based on such historic data, 1,000 per million primary vaccinees would experience severe adverse events, and 14 to 52 individuals per million primary vaccinees would experience life-threatening reactions to the vaccine (i.e., eczema vaccinatum, progressive vaccinia, and postvaccinal encephalitis), and 1 or 2 people would die (CDC, 2003g). Although recent smallpox vaccination has been associated with adverse events affecting the heart (discussed in Chapter 3), studies of death certificates of vaccine-associated deaths were conducted in 1959-1966 and in 1968 did not find deaths associated with cardiac complications (CDC, 2003f).

The vaccine’s side effects are known to include malaise and fever that could interfere with a person’s ability to work, therefore raising questions about the need for time off, with implications for the workforce and for staff scheduling. In the dilution study of Aventis Pasteur vaccine, 25 percent of volunteers missed regularly scheduled duties due to vaccine-related symptoms (Talbot et al., 2004).

Because of those safety concerns and the changed risk-benefit balance in the face of the limited number of cases of disease, the United States ceased general vaccination in 1972, several years before smallpox was officially declared eradicated. After the terrorist attacks of 2001, the safety of the vaccine came into focus as one of the most significant factors in decision-making (see below). Smallpox vaccination plans included vaccinia immune globulin (available in very limited quantity in 2002) and cidofovir as first- and second-line therapies, respectively, for treatment of serious vaccine-related complications (CIDRAP and IDSA, 2004; CDC, 2003h).



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