Smallpox is estimated to have killed between 300 and 500 million people in the twentieth centuryalone. About 30% of unvaccinated victims die (some sources suggestup to 50%). Although the vaccinia vaccine is very effective at preventing smallpox, it is not without risks. Its complication rate is higher than that associated with anyroutinely used vaccine. This technological barrier wouldbe much lower for a terrorist. Some experts believe that it isvery unlikely that Iraq has smallpox since they did not use it during the Gulf War. Policy Implications

Although most experts deem the risk of a smallpox attack to be very low, the high consequences of a release have led the President to order the vaccination ofapproximately 500,000 people in the armed forces and to initiate a voluntary program to encourage as many as 10million medical workers and first respondersto be vaccinated. The United States is helping to increase the security of the former Soviet Union's biological weapon stockpiles. For a comprehensive discussion of these programs, see CRS Report RL31368(pdf) PreventingProliferation of Biological Weapons: U.S. Assistance to theFormer Soviet States .
Smallpox, which kills approximately 30% of its victims, is estimated to have killedbetween 300 and 500 millionpeople in the twentieth century before the World Health Organization's successful eradication program. Thesmallpox vaccine is effective at preventingsmallpox but has a higher complication rate than any other currently used vaccine. The terrorist attacks of 2001have increased fears that smallpox might beused as a weapon of terror. Smallpox has several properties that might make it desirable by terrorists, such ascontagiousness and high lethality. These factorsand its limited availability also make it difficult for a terrorist to use. Most experts agree that it is very unlikely thatsmallpox will be used as a weapon, but thehigh consequences of a successful attack have prompted exploration of methods to counter this threat. Also seeCRS Report RL31694 Smallpox VaccineStockpile and Vaccination Policy and CRS Report RL31368(pdf), Preventing Proliferation of BiologicalWeapons: U.S. Assistance to the Former Soviet States. This report will updated as warranted.