Table 2.

The comparison of VARV, MPXV, and SARS-CoV-2 in epidemiology and transmissibility.

	Host tropism	Transmission route	R0	References
VARV	Narrow (humans are the sole host)	Respiratory route and contact transmission	5.0–7.0	[11], [44]
MPXV	Broder (infects mammalian species like humans, nonhuman primates, and rodents)	Close contact with infectious substances or via respiratory droplet particles to transmission	0.6–1.0	[14], [24], [25], [29], [30], [31], [45], [46]
SARS-CoV-2	Broder (including humans and a variety of animals, like bats, pangolins, minks, or other animals)	Close contact, respiratory route, and aerosol transmission	Original strain is between 1.4 and 3.9; Delta strain is 5.1; Omicron BA.1 is 9.5; BA.2 is 13.3, and B.A. 4/5 is much higher (18 is not a correct estimation)	[47], [51], [52], [53], [54], [55]

Abbreviations: R₀ = the primary case reproduction number; VARV = variola virus; MPXV = monkeypox virus; SARS-CoV-2 = severe acute respiratory syndrome coronavirus 2.