In a situation like the Deuterium Bottleneck, if the availability of deuterium is too low then the necessary nuclear fusion does not happen. (See link below for BigBang Nucleosynthesis). This can be used as a comparison to the spread of a virus. (One can also use as an example -The Plasmodium bottleneck: malaria parasite losses in the mosquito vector -Wiki)
Let's assume you live in a village with 1000 people. Take the average value of R0* as 2.2 (calculated from various WHO-sanctioned studies) and the number of infected people on Day 1 as just 1. Let's also assume that everyday 2.2 people will be infected for certain.If we calculate the total number of infected people on Day 2, it would amount to 1 + 2.2 = 3.2. This would result in the number of people infected per day increasing to 1005 by Day 09. Therefore, by this time, all 1000 people in your village are already infected. But incubation period is 2-14 and not everyone will show the symptoms.
Below graph will show if the original value multiply by 2, 4,8,32 etc and (lower blue) and if we add the previous days figure (orange)
Now, let's take a lower value of R0 = 1.5. Using this value, we can work out that all 1000 people will be infected by Day 18.
If we apply the worldwide death rate (5.5%) to the village of 1000 people, 55 of them will have died from the virus. Its incubation period is 2-14 days. If we were to lock down the whole village on Day 5 and prevent any contact between people, the virus would reach its bottleneck. After initial infection, it will not be able to infect anyone again. Therefore, if we test everyone else and advise healthy people to stay away, the total number of deaths could shockingly be reduced to only 1 or 2.
However, these figures could vary for many reasons. For example, some people may hide their infected status or just not volunteer to be tested (as seen in some cases in Sri Lanka). In that case, the virus will keep spreading, but will be significantly mitigated by the lock-down.
However, virus will stop spreading once when movement of people restricted and when the most serious cases would not recover. Those who will recover will have the immunity from the Covid-19.
We can apply this model to a city with 100000 people. With complete lock-down only 1-2 people will die for every 1000. You will have 100-200 deaths and if it is one million you will have 1000-2000 deaths. But to get that result we assume a city should be totally lock down for at least 2 cycles of incubation period (28 days) banning all movement.
Countries adopting this type of model successfully are China, South Korea and Germany. In Sri Lanka's case there are lot of patients still unaccounted for which hinder the effect of lock-down.
*basic reproduction number (see link below)
Formula used - ((1-R0n)/(1-R0)) , n is the day
(Special help - Shakyra Dharma)
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