In The Demon in the Freezer, Richard Preston accounts the history and background of the smallpox virus and the threats it poses to us in the future. The virus first became known to humans between 3,000 and 12,000 years ago when it infected a human from its original animal host and continued to plague humans for years to come. Smallpox is characterized by the formation of blisters filled with pus that emerge through a victim's skin known as pustules. The pustules cause a great deal of pain and severely hinder an infected person. Many victims of the virus die due to unknown reasons, but some survive and their pustules scab and fall off. The smallpox virus comes in two forms, Variola minor and Variola major. Minor is a weak mutant of the virus that most victims survive whereas major usually kills one-third of its victims, although the death rate can be (and has been) much higher during outbreaks since a very small percentage of the population is vaccinated against the virus. Very few people are vaccinated nowadays and very few doses of vaccinations are on hand because the smallpox virus was eradicated in 1977 and is no longer considered a threat. Dr. D. A. Henderson is widely credited with the eradication of this deadly virus as he headed the World Health Organization's (WHO) Smallpox Eradication Unit from 1966 until 1977, just before Rahima Banu came down with the last documented case of Variola major. Henderson's team was able to eradicate the virus by studying the wave nature of outbreaks (due to the incubation period of the virus) and vaccinating people around an outbreak in a method known as surveillance and ring vaccination. Now the virus officially resides only in two labs in the world: the CDC in Atlanta and Vector in Novosibirsk, Russia. However, it is widely believed that the virus lives unofficially in biological warfare labs throughout the world and that many other nations are trying to acquire the virus for their own research and development of weapons.