The Wuhan virus, first described as not very dangerous, appears to have a troubling characteristic: it is highly infectious.
We know how quickly an epidemic spreads by knowing its basic reproduction number (R0) – the number of infections one infected person generates on average during the infectious period. According to a preliminary paper by researchers at Hong Kong Polytechnic University, the University of Hong Kong and Shanghai Normal University, the Wuhan coronavirus has a reproduction number between 3.30 and 5.47.
For instance, if we assume an R0 of 5 and an infectious period of one week, each infected person will on average infect 5 other persons within a week. Assuming there is no quarantine, 2000 infected patients will grow to 10.000 a week later, to 50.000 two weeks later, to 250.000 within three weeks, and to 1.250.000 within a month.
Influenza has an R0 of 2-3, Ebola 1.5-2.5. The Wuhan virus basic reproduction number (3.3 – 5.5) is closer to SARS, which had a basic reproduction number of 2-5 and caused around 8000 cases with nearly 800 deaths.
The currently confirmed 2000 cases infected with the Wuhan virus are in quarantine. More troubling are the numbers of suspected cases. In Chinese mainland cities, numbers of suspected cases are not released. These numbers are, however, published in Hong Kong, where there are 5 confirmed and 244 suspected cases.
How many actual cases there are is unclear. If we take the Hong Kong ratio of reported and suspected cases and apply this to other Chinese cities, there would be around 96.000 suspected cases. If we assume a reproduction number of 4 (the average of the Hong Kong Politecnic preliminary report) and a time of one week, this number would grow to 1.5 million cases within two weeks, and to around 25 million cases within 4 weeks.
The Center for Systems Science and Engineering at Johns Hopkins University estimates that, as of January 26th, there are over 20.000 cases. However, they suggest that the incubation period may be longer than assumed and asymptomatic infections might prove capable of spreading the virus, in which cases their estimate would be too low.
What makes the Wuhan virus especially difficult is that it appears to have an incubation period of up to two weeks, a time during which no symptoms can appear, but others are nevertheless infected. As long as no symptoms appear, cases cannot be quarantined and go on to spread the epidemic.
Why would that be of interest for design and innovation? The principles behind epidemics can help to explain other phenomena as well – the spread of a hype for a brand or product or of ‘fake news’, for instance. The priciples are straightforward, but modeling them is exceptionally difficult as these are dynamic systems with many unknowns. On January 25th, the sheer number of cases of Wuhan coronavirus varied between 500 (the official number), 20.000 (the estimate by Johns Hopkins CSSE) and 44.000 (the estimate by the Institute of Public Health Medicine at the University of Hong Kong).
Update, January 28: While there have been around 500 officially confirmed cases on January 22, on January 28 this number grew to 4.500 official cases. We don’t know the actual number of cases, but we can see the exponential nature of the spread of the epidemic.