Sunday, May 10, 2020

Covid-19 Coronavirus Fate: Muller's Ratchet

Such viruses tend to accumulate mutations over time that make them less virulent.
Mutations tend to be dysfunctional rather than beneficial.

So, slowing down the transmission should weaken the virus strain.

See also Farr's Law, which also includes a decreasing infectivity over time, beyond the reduction of susceptibles in the population at risk:

A century ago John Brownlee showed that Farr's law gives an exponential function:

I(t) = exp[-At^2 + Bt + C] = exp(C) exp[-At^2 + Bt]

this is a constant term times an exponential term of growth (Bt) and one of decrease (-At^2).

From the beginning, t near zero, to the end, t >> 1  or -At^2+Bt << -1, I(t) looks somewhat like the bell-shaped curve of the Normal, Gaussian, statistical distribution, exp(-a(t-b)^2).

Setting  -At^2+Bt << -1 lets one predict the effective end of the epidemic, given A and B from fitting the curve function  to the data.

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