May 2010 marked the 30th anniversary of the World Health Organization’s declaration that the world had won freedom from smallpox. An intensive two-year search had discovered no evidence of the disease since the last case on 26 October 1977. It was a historic moment — no disease had ever before been eradicated. Smallpox had terrorized humans for more than 3,500 years and in the 20th century alone had been responsible for 300 million deaths. The success of the…