Smallpox, an acute and contagious disease caused by the Variola virus, has historically been one of the most destructive scourges upon humanity. This member of the Orthopoxvirus family was responsible for devastating epidemics for centuries across the globe. Characterized by a severe systemic illness followed by a distinctive rash that often left survivors scarred or blind, the disease had a mortality rate of up to 30% for the major strain. The profound threat smallpox posed made the search for prevention a paramount public health necessity.
The Historical Foundation: Variolation
Before the advent of modern science, variolation was the only known method to mitigate the severity of a future smallpox infection. This practice originated centuries ago in regions of Asia and Africa. The procedure involved taking infectious material, such as dried scabs or pus, from a person experiencing a mild case of smallpox.
This material was then deliberately introduced into the skin of a healthy individual, often through a scratch or nasal insufflation. The goal was to induce a localized, milder form of the disease, usually caused by the less severe Variola minor strain. While this process carried a significant risk, resulting in 1–2% of those inoculated dying from the infection, it was a major improvement over the 30% fatality rate of naturally contracted smallpox.
The Definitive Prevention: The Smallpox Vaccine
The practice of variolation was superseded by a safer and more reliable prevention method developed by the English physician Edward Jenner in 1796. Jenner observed that milkmaids who had contracted cowpox, a mild disease from cows, appeared to be protected from smallpox. He hypothesized that the mild animal disease could confer immunity against the human disease.
Jenner tested his theory by inoculating a young boy with material from a cowpox lesion. After the boy recovered from the mild cowpox illness, Jenner intentionally exposed him to smallpox, and the boy showed no signs of the disease. The protective agent was the cowpox virus, or Vaccinia virus, which is closely related to Variola virus. This method, which Jenner termed vaccination, successfully induced an immune response through cross-protection, allowing the immune system to neutralize the deadly smallpox virus. This revolutionary technique offered protection without the risk of causing or spreading the human disease.
Global Strategy: Achieving Eradication
The existence of an effective prevention method laid the groundwork for an ambitious global effort. In 1967, the World Health Organization (WHO) launched the Intensive Smallpox Eradication Programme, targeting the remaining endemic countries. The initial strategy of mass, blanket vaccination proved logistically difficult and inefficient in many densely populated regions.
The program’s success came from a shift to a targeted epidemiological approach called “surveillance and containment.” This strategy relied on rapid identification of a smallpox case through active searching, followed by immediate isolation of the patient. Public health teams then performed “ring vaccination,” a highly targeted intervention.
Ring vaccination involved vaccinating everyone who had been in close contact with the infected person, and subsequently vaccinating the contacts of those contacts. This created a ring of immune individuals around each new case, which effectively cut off the chains of transmission. Because smallpox required prolonged, face-to-face contact to spread, this localized strategy proved highly efficient at stopping outbreaks worldwide.
Current Status and Preparedness
The last naturally occurring case of smallpox was recorded in Somalia in 1977, and the WHO officially declared the disease globally eradicated in 1980. This public health triumph meant that routine childhood vaccination was discontinued in the United States and many other nations by the early 1970s. Consequently, the average person no longer requires protection against the disease.
However, biosecurity concerns remain regarding the official laboratory stocks of Variola virus maintained in secure facilities in the United States and Russia. Due to the potential for unauthorized release or bioterrorism, national health authorities maintain a strategic stockpile of modern vaccines for emergency deployment.
Two modern vaccines are available for this purpose, including ACAM2000, which is a live, replicating Vaccinia virus vaccine. A newer, non-replicating vaccine called Jynneos (Modified Vaccinia Ankara) is also stockpiled, offering a safer alternative for people with compromised immune systems. These vaccines ensure that a targeted preventative response can be mobilized rapidly should the disease ever reappear.