How contagious is the Coronavirus (RO)?

The attack rate or transmissibility (how rapidly the disease spreads) of a virus is indicated by its reproductive number (Ro, pronounced R-nought or r-zero), which represents the average number of people to which a single infected person will transmit the virus.

WHO's estimated (on Jan. 23) Ro to be between 1.4 and 2.5.

Other studies have estimated a Ro between 3.6 and 4.0, and between 2.24 to 3.58.

Preliminary studies had estimated Ro to be between 1.5 and 3.5.

An outbreak with a reproductive number of below 1 will gradually disappear.

For comparison, the Ro for the common flu is 1.3 and for SARS it was 2.0.

 
Fatality Rate (case fatality ratio or CFR) of the Wuhan Coronavirus

The novel coronavirus' case fatality rate has been estimated at around 2%, in the WHO press conference held on January 29, 2020. However, it noted that, without knowing how many were infected, it was too early to be able to put a percentage on the mortality rate figure.

A prior estimate had put that number at 3%.

The fatality rate can change as a virus can mutate, according to epidemiologists.

For comparison, the case fatality rate for SARS was 10%, and for MERS 34%.

 
The incubation period (how long does it take for symptoms to appear)
Symptoms of COVID-19 may appear in as few as 2 days or as long as 14 (estimated ranges vary from 2-10 days, 2-14 days, and 10-14 days), during which the virus is contagious but the patient does not display any symptom (asymptomatic transmission).

 
Age and conditions of Coronavirus cases
According to early estimates by China's National Health Commission (NHC), about 80% of those who died were over the age of 60 and 75% of them had pre-existing health conditions such as cardiovascular diseases and diabetes.
According to the WHO Situation Report no. 7 issued on Jan. 27:

The median age of cases detected outside of China is 45 years, ranging from 2 to 74 years.
71% of the cases were male.
A study of 138 hospitalized patients with NCIP found that the median age was 56 years (interquartile range, 42-68; range, 22-92 years) and 75 (54.3%) were men.
The WHO, addresses the question: "Does the new coronavirus affect older people, or are younger people also susceptible?" by answering that:
  • People of all ages can be infected by the novel coronavirus COVID-19.
  • Older people and people with pre-existing medical conditions (such as asthma, diabetes, heart disease) appear to be more vulnerable to becoming severely ill with the virus.

Age and Sex of the first deaths as reported by the China National Health Commission (NHC)
The NHC reported the details of the first 17 deaths up to 24 pm on January 22, 2020. The deaths included 13 males and 4 females. The median age of the deaths was 75 (range 48-89) years.

WHO Risk Assessment: Global Emergency
On January 30, the World Health Organization declared the coronavirus outbreak a Global Public Health Emergency.

For more information from the WHO regarding novel coronavirus: WHO page on Novel Coronavirus (2019-nCoV).
 
Comparisons:
  • Every year an estimated 290,000 to 650,000 people die in the world due to complications from seasonal influenza (flu) viruses. This figure corresponds to 795 to 1,781 deaths per day due to the seasonal flu.
 
  • SARS (November 2002 to July 2003): was a coronavirus that originated from Beijing, China, spread to 29 countries, and resulted in 8,096 people infected with 774 deaths (fatality rate of 9.6%). Considering that SARS ended up infecting 5,237 people in mainland China, Wuhan Coronavirus surpassed SARS on January 29, 2020, when Chinese officials confirmed 5,974 cases of the novel coronavirus (2019-nCoV). One day later, on January 30, 2020, the novel coronavirus cases surpassed even the 8,096 cases worldwide which were the final SARS count in 2003.
 
  • MERS (in 2012) killed 858 people out of the 2,494 infected (fatality rate of 34.4%).