Why Covid-19 is not going anywhere anytime soon

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

04 October 2020

Having carefully observed how my three children stopped wetting their beds, I have come to the conclusion that bedwetting never stops! The duration between wet nights keeps increasing and eventually, it is so long that, for most people, life ends before the next event.

The child will have one dry night, then two consecutive ones, then three…then a week… and so on until eventually he goes through many years without wetting the bed. If he lives long enough, the next wet night might come in his 80s! Well, that’s my postulate on the matter – I might be completely wrong.

However, it brings out the concept of exponential decays. The best illustration of this is the float valve commonly found in water tanks and toilet cisterns. Its job is to stop the water from flowing in once the tank has filled up.

But, unbeknownst to most people, this valve never ever stops the flow completely; it always leaks. The reason is this: the higher the level of the water, the narrower the valve opening.

As the valve opening gets narrower, the rate of flow reduces. The water can only stop flowing if it reaches it maximum height. But the float valve cannot allow that height to be reached.

Think about it this way: suppose you wanted to travel from point A to B. You start by travelling half the distance; then you travel a half of the remaining journey. If you continue in this fashion, each time moving only a half of what is remaining, would you ever reach point B?

Of course not; because there is no instance when you cover the entire remaining distance. You get closer and closer but you will never arrive at B.

It is the same with the water: it gets closer and closer to the maximum height but never gets there. Since the float valve can only shuts the flow completely at the maximum height, then it is clear to se that it will always have a leak.

This kind of behaviour is technically called an exponential decay. The rate of flow of the water dies off exponentially and never, ever reaches zero.

Disease outbreaks also exhibit exponential growth and decay. In the decay phase, the number of infections gets smaller and smaller but never reaches zero. Indeed, I only know one disease that has been eradicated by human intervention – smallpox. With that in mind, do not expect covid-19 to be eliminated any time soon.