Table. Evidence on transmission dynamics of human infections with 2019-nCoV, as at 22 January 2020.
| Observation | Date | Interpretation | Supports Scenario 1?a | Supports Scenario 2?b |
|---|---|---|---|---|
| By 20 January, 198 laboratory-confirmed cases, 3 fatal, 25 recovered [28] | 20 Jan 2020 | Fatality risk among hospitalised cases is 11%c | Yes | Yes |
| No infections among the more than 700 people under medical surveillance, including HCWs [28] | 20 Jan 2020 | Very low human-to-human transmissibility | Yes | No (Note: assuming adequate contact tracing and surveillance) |
| Only one likely human-to-human cluster among the first 41 cases [18] | 20 Jan 2020 | Very low human-to-human transmissibility (R 0 of 0.02) | Yes | No (Note: assuming adequate contact tracing) |
| Only approximately 70% of the first 41 cases had exposure to Southern China Seafood Wholesale Market [16] | 15 Jan 2020 | Low human-to-human transmissibility (R 0 of 0.3) | Yes | No (Note: possible selection bias towards identifying cases linked to that market) |
| New cases with a travel history to Wuhan before onset were confirmed in other cities in China [29] | 20 Jan 2020 | Indicative of many mild to moderate infections (not requiring hospitalisation) in Wuhan | Yes | Yes |
| Four exported cases to other countries, all with relatively mild illness [30,31] | 12–20 Jan 2020 | Indicative of many mild to moderate infections not necessitating hospitalisation or outpatient medical care in Wuhan | Yes | Yes |
| Four exported cases, at least three of whom had no contact with Southern China Seafood Wholesale Market [30,31] | 12–20 Jan 2020 | At least some limited human-to-human transmission (unclear R 0) | Yes | Yes |
| Two family clusters in Guangdong, with family members who did not visit Wuhan but were infected after the other family member(s) returning from Wuhan were confirmed with the infection [29] | 20 Jan 2020 | At least some limited human-to-human transmission (unclear R 0) | Yes | Yes |
| 15 HCWs confirmed with infection of 2019-nCoV (not clear whether infections were from one case or multiple cases) [20] | 20 Jan 2020 | Super-spreading event? Could still be consistent with limited human-to-human transmission if an isolated incident (unclear R 0) | Yes | Yes |
| Exported cases identified in Taiwan and the United States with illness onset dates on 11 and 19 January [32,33] | 22 Jan 2020 | Could be because of surveillance bias, but is more consistent with an increase in incidence of infections over time | No (Note: possible selection bias because of enhanced surveillance towards identifying more recent cases) | Yes |
HCWs: healthcare workers; nCoV: novel coronavirus; MHC: Municipal Health Commission.
a Most infections are zoonotic with limited human-to-human transmission (R 0 < 1).
b Initial zoonotic spillover with efficient human-to-human transmission (R 0 > 1).
c Estimated as (fatal cases) / (fatal cases + recovered cases).