Table 1

Mode of introduction		Category	Mechanism	Conclusions of Pathway Analyses
Mode of introduction		Category	Mechanism	Relative likelihood (low/medium/high)	Trend
Accidental reintroduction	Biosafety incident at a known WHO repository	A	Laboratory acquired infection or accidental release from WHO repository (restricted to CDC and Vector)	Low	Decreasing
	Biosafety incident outside of a known repository	B1	Unknown, archived and untested/misdiagnosed clinical sample	Low	Decreasing
		B2	Unknown, archived and tested, but unlabeled sample	Low	Decreasing
		B3	Rediscovered sample labeled as smallpox	Low	Decreasing
	Environmental resurrection / mutation	C1	Archived outside of the lab	Low	Decreasing
	Environmental resurrection / mutation	C2	Natural orthopox mutation into virus that can cause smallpox-like illness	Low	Constant
Deliberate reintroduction	Biosecurity incident: theft from a known repository	D1	Insider theft	Medium	Constant
		D2	Outsider theft	Medium	Decreasing
		D3	Collusion	Medium	Constant
	Biotechnology	E1	De novo synthesis	Medium	Increasing
	Biotechnology	E2	Deliberate mutation of a related orthopox virus	Medium	Increasing
	State illicit weapons program	F1	State retained it post-eradication and post-consolidation of smallpox samples into 2 repositories	Low	Constant *
	State illicit weapons program	F2	State acquired it post eradication: accidental discovery, acquired from other state program, theft from repository, biotech	Low	Constant+

The table lists potential pathways for accidental or deliberate release of smallpox virus. See text for further details on mechanisms and associated relative likelihood. * Security experts disagree as to how this may change over time, as discussed in the paper. + Most of these pathways are decreasing, but the biotech pathway is expected to increase with time.

Table 1: Main pathways for possible recurrence of smallpox.