Likelihood of Smallpox Recurrence.

The 30 year anniversary of the eradication of smallpox was recently celebrated and represents a major achievement in international public health. However, the likelihood of re-introduction of eradicated diseases is expected to evolve with time, and warrants continued assessment. Using influence diagrams to structure the analysis, this paper seeks to systematically examine the various pathways that could lead to accidental or deliberate introduction of a novel or eradicated pathogen using smallpox as an example. The accidental reintroduction of smallpox may occur through three main pathways: Biosafety incident at a known repository, biosafety incident outside of a known repository, and environmental resurrection. The deliberate reintroduction can also be subdivided into three main pathways: Biosecurity incident at a known repository, illicit state biological weapons program, and synthesis using the tools of modern biotechnology. We conclude that the likelihood of recurrence of an eradicated agent, such as smallpox, is small, but ultimately unknown and expectedly increases with time primarily due to the rapid advancement of biotechnology.