Table 1–2.
Pathogen adaptation and pandemic risk.
| Stages | Transmission to humans | Type of pathogen | Route of transmission |
|---|---|---|---|
| (1) Transmission to animal reservoir only | None | H3N8 influenza virus | |
| (2) Primary infection | Only from animals | Anthrax | ![]() |
| (3) Limited outbreaks | Limited human-to-human transmission chains | Marburg virus | ![]() |
| (4) Sustained outbreaks | Many human-to-human transmission chains | H1N1influenza virus | |
| (5) Predominant human transmission | Human-to-human | Smallpox virus |
Source: Adopted from Jamison DT, Gelband H, Horton S, et al., Disease Control Priorities: Improving Health and Reducing Poverty. 3rd edition. Washington (DC): The International Bank for Reconstruction and Development/The World Bank; 2017 Nov 27 under the Creative Commons Attribution 3.0 IGO license (CC BY 3.0 IGO).

