Monday, May 25, 2020

What's the Actual Doubling Rate of Covid-19 & Number of Days for Herd Immunity?

I refrained from doing any analysis on Covid-19 pandemic owing to its complexity and the seriousness of the issue. 
Perhaps, everything has a life and I had to give a chance to analysing the coronavirus data. A bit of disclaimer : this is not going to be a dashboard or predictive in nature. 

After hearing a lot about the doubling rate of last 3 days, previous week, last 10 days and what not, I decided to dig deeper and find out the actual doubling rate. 

Let's understand where I am coming from. If the number of infected case goes from 1 to 2, it has doubled, if it has gone from 2 to 4 it has doubled again, 4 to 8 means another round of doubling, and so on, we all know where this is heading towards.


To make it more clear, if we have total number of infected cases equal to 32 we have doubled 5 times(25=32). 





As you can see above that India's total detected infection count has doubled 17 times and at an average rate of ~6/7 days, way different than the 10/12/15 days doubling rate floating around in media. I must add that last few doubling iterations have taken longer time which is a good sign. 

So, what we are doing is that taking the total no. of days and dividing it by total number of doubling iterations. In other words, taking total number of days as 116 and dividing it by # of doubling iterations, which is 17, gives us ~7 days. The Cumulative doubling column in the chart above is calculated in the same way, for calculating the average doubling rate till that number of iterations(Days/Doubling iteration)





 So, how long can this continue? What's the end game?
Taking India's population as roughly 1.38 billion we can't double beyond 30 times as 231 is greater than 1.38 billion. This means beyond 30 doubling instances everybody gets infected with Covid-19. Scary!

Obviously, we can't go that path. The doubling rate will significantly drop over the course of this situation we are in, which can also be checked in the graph above, blue line overshooting the plateau red one. What about the herd immunity argument? 

Taking 6 Day doubling rate entire country would get infected in 84 days and 98 days is needed with 7 Day doubling rate. If we take the most recent doubling rate of 13 days, it would take 182 days or roughly 6 months for all of India to get infected. 

If we go by Wikipedia for sake of simplicity, herd immunity requires anything in the range 29%-74% of the population to get infected . You can check how many days it would take to cross that threshold above in the chart. I would still write it down.

With 6 Day doubling rate, 72 days & 78 days are respective numbers for 29% & 74% requirement.
With 7 Day doubling rate, 84 days & 91 days are respective numbers for 29% & 74% requirement.
With 13 Day doubling rate, 156 days & 169 days are respective numbers for 29% & 74% requirement.


If you are careful you can see the subtle predictive aspect of this analysis too but I would not like to get into that. 
Keep watching this space as I would be adding more content on the Covid-19 Coronavirus pandemic situation. 


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