Table 1. Viability of infectious variola virus in various materials*.

Study, year, (reference)	Type of material	Storage conditions	Maximum storage time viable virus was recovered†
Downie and Dumbell, 1947 (18)	Lesion crusts	Room temperature, exposed to daylight	196 d
		Room temperature, kept in dark	417 d
		Refrigerated and then room temperature, exposed to light	>196 d after refrigeration, >341 d total)
		Refrigerated and then room temperature, kept in dark	>196 d after refrigeration, >341 d total)
		In a vacuum over calcium chloride	782 d
	Saline extract of crusts	Refrigerated	432 d
	Vesicle fluid on glass slides	Room temperature, exposed to daylight	35 d
		Room temperature, kept in the dark	84 d
	Vesicle fluid diluted in broth	Refrigerator	270 d
MacCallum and McDonald, 1957 (19)	Crusts embedded in raw cotton	Room temperature, indirect light	530 d
		30°C, kept in the dark, 58%, 73%, and 84% relative humidity	70, 70, and 60 d, respectively
Wolff and Croon, 1968 (20)	Crusts	Room temperature, kept in an envelope	4,745 d (13 y)
Huq, 1977 (21)	Crusts	35°C, 65%–68% relative humidity	21 d
		26°C, <10% and 85%–90% relative humidity	84 and 56 d, respectively
		4°C, 10% and 60%–62% relative humidity	112 d
		−20°C	112 d
Rao, 1972 (15)	Vesicle fluid on glass slides	Direct sunlight	<1 h
	Vesicle fluid in capillary tubes	Direct sunlight	<2 h

*Specimens from patients with smallpox were used for all studies.
†For several studies, this is the last sampling time point and either no material was left to continue the experiment or no further samplings were conducted.