Infection efficiency, transmissibility.

Capacity to survive outside the human body (including in aerosols, in droplets, on surfaces, in stools, in intermediate animal hosts, etc.)

Potential to shed virus from an infected person, asymptomatic or diseased.

Genetic stability or variability (affecting the potential of long-lasting immunity).

Viral load determines the incubation period with the formula high load ->short incubation period ->high severity.

Human susceptibility to the virus; transfer of parental immunity to newborns.

Route and efficiency of human-to-human transmission.

Presence and capacity of asymptomatic carriers to transmit the virus.

Immunity created after infection, its robustness and how long-lasting it is.

Severity and duration of the disease: proportion symptomatic, lethality (CFR).

Pathogenicity and disease spectrum; disease pattern according to age and comorbidities, and related potential to spread.

Temperature, humidity and seasonal changes in climate affecting the stability and transmission potential of the virus and human susceptibility.

Increasing extreme weather conditions such as droughts and severe storms, as well as global climate change may also affect transmission patterns.

Air pollution may also play a role in the transmission and stability of the virus.

Demographic variables such as population density, age structure and household composition.

Mixing patterns within households, including bed sleeping patterns, related to housing conditions and hygiene practices.

House construction with solid walls or permeable walls (thatched walls, straw mats).

Mixing patterns among households related to settlement patterns: social networks, urban–rural differences, working conditions, religious practices and commuting patterns.

Variables related to built environments, road infrastructure and socioeconomic conditions.

Mobility between communities, including international travel.

Crowding institutions: for example, elderly homes, extended families, boarding schools, child institutions, seclusion during tribal ceremonies, hospitals, nursing homes, military barracks and prisons.