R(0) & The Real Numbers

The daily cases of positive SARS-CoV2 are rising in several states. Newspapers and Govt. channels are providing the total positive cases detected daily. However, a visibility on the total burden of positive cases is not available despite knowing the daily stats. Often, it is erroneously thought that the cumulative numbers are less.

In this blog, I have talked about the incidence and prevalence of the persons affected that are shedding the viruses in the community, both from the symptomatic and asymptomatic perspective. The average number a symptomatic patient sheds virus and the average number an asymptomatic person sheds the virus is based on the the referenced scientific data. The details are mentioned in this blog.

This blog provides us a perspective on the cumulative cases within a community as well as how long should we continue lock down amidst the airborne nature of the virus.

Let me explain the concept of incidence and prevalence.

Incidence is the new cases occurring in that period, whereas prevalence is the cumulative cases existing during that period. If I presume the incidence at the time of collection of the swab is 10,000, and the asymptomatic is 5x to 10x (let us call it A), the total burden of positive cases is in that proportion.

If we are to presume the disease persists for 14 -21 days in its mild form, then the prevalence now is 14x-21x the multiple of A. If I go by some researchers, the asymptomatic shed the virus for 21-28 days.

That’s the total burden of test-positive cases.

Airborne precautions are likely to be scaled up on the risk stratification. All those risk color charts floating around are likely unreliable for this simple reason. To make it simple, I will just make two categories –


Non-essential are all those without which we can survive.

You may naturally ask, until when should we live like this? It’s not too long, vaccines and drugs are on the horizon. Also, though the virus is still aggressive, it will likely become less aggressive in the future. So, let’s wait before taking an unrequired risk.

Shashank Heda
Dallas, Texas

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