A pathogen’s harmfulness is determined by the combination of Ro (reproductive number) and the case fatality rate.
How contagious is coronavirus? (Reproductive Number (Ro) of 2019-nCoV)
The novel coronavirus' reproductive number (Ro, pronounced R-nought or r-zero), which measures how rapidly a disease spreads, is estimated between 2.0 and 3.1, according to preliminary studies [5][6]. Another study provided a similar estimate of 2.6 with an uncertainty range of: 1.5-3.5[7]. The WHO noted on January 23 that human-to-human transmission was occurring and a preliminary R0 estimate of 1.4-2.5[13].
For comparison, the RO for the common flu is 1.3 and for SARS it was 2.0.
Ro represents the average number of people who will catch the disease from a single infected person, so if R0 for coronavirus is 3.8, it means that on average every case of Wuhan coronavirus would create between 2 and 3 new cases.
Fatality Rate (case fatality ratio or CFR) of 2019-nCoV
The novel coronavirus' case fatality rate is currently estimated at around 3%[9] (between 2% and 4%).
For comparison, the case fatality rate with seasonal flu is less than 0.01% (1 death per every 10,000 cases)[7].Fatality rate for SARS was 10%, and for MERS 34%.
Incubation Period (how long it takes for symptoms to appear)
The Wuhan novel coronavirus appears to be contagious before symptoms appear, as it is estimated to have an incubation period of 10 to 14 days, according to Ma Xiaowei, the director of China’s National Health Commission[11].
The United States' CDC estimates the incubation period for 2019-nCoV to be between 2 and 14 days [10].
This means that symptoms of the novel coronavirus (2019-nCoV) may appear in as few as 2 days or as long as 14, during which the virus is contagious but the patient does not display any symptom.
WHO Risk Assessment
China: Very High
Region: High
Global: High
Not a Public Health Emergency of International Concern (PHEIC)
The WHO hasn't declared the outbreak an international health emergency. The WHO emergency committee has convened twice [13] (on January 22, and January 23) and has twice declined to make such a declaration.
Diferentemente do que tem acontecido com os países que lideram o ranking de números absolutos de casos e mortes por , são os países menores que apresentam a pior taxa relativa de casos e mortes por milhão de habitantes – o que, concretamente, chega a ser pior. 

No caso dos óbitos, a pequena San Marino tem 1.619 mortes por milhão de habitantes, ficando em 1º lugar no ranking relativo. Já os Estados Unidos (EU), primeiro lugar no ranking em número absoluto, tem “apenas” 979 óbitos por milhão, uma taxa 40% inferior. 

Já no ranking de casos relativos dentro por milhão de habitantes, a lista é liderada pela pequena Andorra, com 98.315 infecções/milhão. Já nos EU esta taxa é cerca de 45% menor: 55.122/milhão. 

Em outras palavras: se os EU tivessem a mesma taxa de óbitos que San Marino, por exemplo, hoje o país teria mais de 535 mil mortes por Covid e não as 324.987 que tem. 

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