# COVID 2020 — A data scientist perspective

Original article can be found here (source): Artificial Intelligence on Medium

# Do not conclude so hastily

From just two graphs let us not make the mistake of concluding. The result maybe reassuring, but is coming from half knowledge, from ignorance and as Herman Melville said

“Ignorance is the parent of fear.”

Let us deshelve the ignorance and the resultant fear. And try data based rational approach. There are many mathematical models to study infectious diseases. The most used and quite simple is the SIR model. The name arises from the fact that it divides the population into three compartments:

* S Susceptible — the ones which can get infection.
* I Infected — the ones infected by the disease and actual carriers.
* R Recovered — the individuals who were infected earlier and now fully recovered (and hopefully have developed immunity to the infection).

Population shifts from Susceptible to Infected to Recovered. I will not bore you with the math behind it, those interested can refer to the link above and code here. Just remember the three compartments defined above, and three more important parameters defined below:

1. Contact Rate — It is a measure of how many persons one infected person can infect-depends on social circle- more social distancing — less is this number.
2. Mean Recovery Rate — It is the reciprocal of the number of days a person stays contagious.
3. Population — The total population.

When we start the whole population is susceptible, and when we finish the whole population is recovered. Below is a sample variation of population from susceptible → infected → recovered.

Remember the model is simple and is not taking death into account. But in real life deaths happen. As we can see from the China data

Before doing the modeling for other countries, since we know that China reached its peak and then started decline, let us see its graph:

The total population of China is 1404 millions, and total population of Wuhan which was the epicenter of this infection is 11 millions.

I see you are calculating only 60,000 from 11 million!! You are forgetting from 23rd January 2020 [Source] China implemented an extensive, stringent quarantine. Something I cannot imagine in my country even in Curfew/Emergency.

Another important thing one may ignore, 60,000 may be a small number from whole population, but they require health services, and China had to build Hospitals to provide health care.

Since the incubation period of Corona Virus can be from 4–28 days [Source], it is possible that there were many asymptomatic carriers in whom symptoms appeared later.

Now let us try and run SIR model in China data, with a initial population of 11 million, that is considering only Wuhan:

Well starting from December 2019, it peaked in mid-February (~ 60 days) and now is on decline. The same trend is visible in the modelled graph above.

So we did hit the Bulls eye with SIR model. Now what, remember the three numbers:
1. Contact Rate,
2. Recovery rate
3. Population

While recovery rate (on an average) will remain same for all countries, what changes is population and contact rate. For the above graph the Population was 11 millions, and contact rate 0.3.

Assuming a country with population of 1000 million becomes susceptible, then if follows the same level of quarantine as China — it will reach peak infection in 80 days and the whole cycle over in roughly 200 days.

An important point overlooked, when talking in numbers is that at peak it will require roughly 75 million hospital beds (assuming 15% of total infected requiring hospitalization) — and may be 10–20% of these will require ICU beds. An in absence of them PEOPLE WILL DIE irrespective of age!! Yes, irrespective of the age- because when breathlessness strikes- hospitals are needed.

To ensure that you have understood what I am saying, let us take the case of Delhi, the capital of India. It has 20 million population. At present the number of cases in Delhi are restricted to 10 cases, there are local transmissions but no cluster transmissions yet reported. The population of Delhi is 20 million and it is host to 172 Hospitals, many of international repute. Assuming each one of the hospitals have a capacity of 1000 (I am indeed exaggerating 😃 ), thus we have 1,72,000 beds capacity.