The statistics behind the Wuhan corona virus

The Wuhan Corona virus is spreading fast with the Chinese new year in full gear but is it time to panic?

In the short term and on the epidemiological front, probably not. But in the longer term and on the economic front, it might well be the straw that breaks the Chinese camel back.

Let's have a quick look at where we stand today, Sunday 26, January 2020 and at where statistics are telling us we may be in a few weeks.

The official number of sick people now close to 2,000 (up from 1,497 earlier this morning) is still relatively low. But this number does not fit with the news coming from China of overwhelmed hospitals. Nor with the more or less complete lock down, as of today, of the city of Wuhan (11 million people) and the severe travel restrictions in the province of Hubei concerning over 56 million people.

The country is facing a "grave situation" Mr Xi told senior officials, according to state television yesterday. With the city of Wuhan building two new hospitals over the coming 10 days specifically dedicated to the pandemic, clearly, the conditions in China are worse than it looks.

Chinese authorities have promised to be transparent, but the precedents are not very good. In 2003, the SARS epidemic was not recognized until very late and then mostly the information was suppressed until the virus petered out in early July of that year.

This time is different in many respects, but mostly for the worst.

First, the good news.

The Wuhan Corona virus has a relatively low R₀ or R naught coefficient, currently estimated at 2.5. This coefficient is very important. It indicates the number of healthy people a sick one will infect while being contagious. If the coefficient is above "1", the virus spreads. 

For reference, these are the R₀ factors of other diseases. The Wuhan Corona virus compares favorably.

Likewise, this R₀ factors is not fixed. The 2003 SARS epidemic started out with a R₀ of about 3 but ended at 0.4 when limitations were enforced.

But the Wuhan Corona virus has other characteristics which makes the situation much more critical. There is no antivirus and the lap between the moment a person becomes infectious and the first symptoms seems to be around a week. This would explain why the Chinese authorities were slow to react but also why the virus may already be more broadly spread out than assumed. Some alarmist estimates say that there may already be over 10,000 cases in Wuhan alone. This sounds extreme but it could be close to the truth and the reason why Chinese authorities are in panic mode.

So where do we go from here?

If you prefer to panic, the best article is from Dr. Eric Feigl-Ding

Dr. Eric Feigl-Ding" I’ll be honest - as an epidemiologist, I’m really deeply worried about this new coronavirus outbreak. 1) the virus has an upward infection trajectory curve much steeper than SARS. 2) it can be transmitted person to person before symptoms appear — I.e. it is silently contagious!"

And he goes on with a long series of tweets which are worth reading since they resume the worst case scenario. (Below, after the article)

But all these alarmist tweets are based on a study from a British Doctor which can be summarized with the following chart showing an explosion of cases over the coming weeks:

Nevertheless, these trends are based on assumptions which may prove to be incorrect and which seems to be based mostly on air travel.

To this, Dr. Stephen Goldstein answered that: "It’s one estimate, with a sketchily narrow CI that the authors have already revised down. Other estimates are lower. This is not 1918, you know that, stop trying to scare people and log off please. Thanks" 

This answer is probably correct. This is clearly not 1918. Nevertheless, now that the opportunity to stop the virus during the initial outbreak was missed, it will clearly be far more difficult and expensive to limit the economic damages in the longer term.

Let's suppose that China does all the right things and that the virus outbreak follows the SARS pattern and goes from 2.4 to 0.4 over the coming 6 months. We will still end up with around 100,000 sick people (which is not a very high number compared to the flu on any given year) and probably 3 to 4,000 casualties which again is a very low number. (Based on the table bellow)

But the economic consequences of the disease on the already slowing down Chinese economy may well be far less mild. Here's an example of the complete blockade of the city of Wuhan as of this morning! (Trains, planes and highways are already closed.)

Beyond the human tragedy of a large city without food and transportation, the banning of tour groups in all of China, interdiction of large assemblies of over 100 people (during the Chinese new year!), closing down of parks, stores and many other amenities, it is the whole Chinese economy which is grinding down to a halt for the new year with no end in sight! 

This in the end may be the real risk of the Wuhan Corona virus. Not that it will become a world pandemic although there is still a small chance that it will, but that it could be the black swan which bring the next recession with a global crash of the world economy and consequences far beyond a mere flu epidemic.


Tweets from Dr. Eric Feigl-Ding"

 1/ "HOLY MOTHER OF GOD - the new coronavirus is a 3.8!!! How bad is that reproductive R0 value? It is thermonuclear pandemic level bad - never seen an actual virality coefficient outside of Twitter in my entire career. I’m not exaggerating...

 2/ “We estimate the basic reproduction number of the infection (R_0) to be 3.8 (95% confidence interval, 3.6-4.0), indicating that 72-75% of transmissions must be prevented by control measures for infections to stop increasing...

 3/ ... We estimate that only 5.1% (95%CI, 4.8-5.5) of infections in Wuhan are identified, and by 21 January a total of 11,341 people (prediction interval, 9,217-14,245) had been infected in Wuhan since the start of the year. Should the epidemic continue unabated in Wuhan....

 4/ we predict the epidemic in Wuhan will be substantially larger by 4 February (191,529 infections; prediction interval, 132,751-273,649), infection will be established in other Chinese cities, and importations to other countries will be more frequent. Our model suggests that..

 5/ travel restrictions from and to Wuhan city are unlikely to be effective in halting transmission across China; with a 99% effective reduction in travel, the size of the epidemic outside of Wuhan may only be reduced by 24.9% on 4 February. Our findings are...

 6/ ...critically dependent on the assumptions underpinning our model, and the timing and reporting of confirmed cases, and there is considerable uncertainty associated with the outbreak at this early stage. With these caveats in mind, our work suggests that...

 7/ a basic reproductive number for this 2019-nCoV outbreak is higher compared to other emergent coronaviruses, suggesting that containment or control of this pathogen may be substantially more difficult.”!!!!

9/ ...cannot be stopped by containment alone. A 99% quarantine lockdown containment of Wuhan will not even reduce the epidemic’s spread by even 1/3rd in the next 2 weeks. Thus, I really hate to be the epidemiologist who has to admit this, but we are potentially faced with...

10/ ... possibly an unchecked pandemic that the world has not seen since the 1918 Spanish Influenza. Let’s hope it doesn’t reach that level but we now live in the modern world  with faster than 1918. @WHO and @CDCgov needs to declare public health emergency ASAP!

11/ REFERENCE for the R0 attack rate (reproductive coefficient) of 3.8 and the 99% containment models come from this paper: https://www.medrxiv.org/content/10.1101/2020.01.23.20018549v1 …

12/ What is the typical R0 attack rate for the seasonal flu in most years? It’s around an R0=1.28. The 2009 flu pandemic? R0=1.48. The 1918 Spanish Flu? 1.80. This new #WuhanCoronavirus reproductive value again? R0=3.8. (Flu reference: https://bmcinfectdis.biomedcentral.com/articles/10.1186/1471-2334-14-480 …)

 13/ ...and it gets even worse, the Lancet now reports that the coronavirus is contagious even when *no symptoms*: specifically: “crucial to isolate patients... quarantine contacts as early as possible because asymptomatic infection appears possible”!

14/ Let’s pretend the 3.8 estimate is too high (there’s unpublished estimates of 2.5). even if this virus’s R0=2.5, that’s still 2x higher than seasonal flu’s 1.28 (ref above), and higher than 1918 Spanish Flu pandemic of 1.80 that killed millions. So 2.8 is still super bad folks

 15) My response to some people who think I’m trying to stoke fear... I’m a Harvard trained scientist with a doctorate in epidemiology (and the youngest dual doctoral grad from Harvard SPH). Here are my response: https://twitter.com/drericding/status/1220999410877898754?s=21 … https://twitter.com/drericding/status/1220999410877898754 …