Covid-19 #1
The maths of infection is simple. First, there is the population, divided into three groups: the susceptibles (S), or those who can be infected, the infected (I) and the recovered (R). The data shape the mathematical model (called SIR, from the groups' initials) necessary to study the infection spread. The fundamental parameter of the model is the value R0, and it is a mathematical term that indicates how contagious an infectious disease is. Specifically, the R0 value tells how many people a person can infect, and it varies from a virus to another. The current estimate for coronavirus is 2.5 (as a comparison, the Spanish flu was around 2.1). At that rate, the infection is exponential: one person infects two people, each of these infects two more and so on. This 'free-for-all' scenario causes a steep rise in the infection curve, to a point in time where the population is entirely infected.
However, that scenario is not acceptable, and not only in terms of lives lost. A country with an almost entire population sick for an uncertain amount of time would not be able to provide the most basic needs: food, energy, public safety, and so on. Also, an attempted quarantine scenario ("we ask you...") would be equally ineffective and an impossible demand to meet by our healthcare.
To stop a pandemic, we must reduce R0 until a value of less than 1. Hence social distancing is fundamental to reduce the infection rate while we 'buy time' to produce new medical equipment, hire hospital staff, and test medicines. The following graphs show the result of a moderate distancing scenario ("we need you to..."), where one person out of four do not follow the rules, and an extensive distancing scenario ("we demand you to..."), where only one of eight violate the lockdown.
The effects are particularly important in countries where healthcare suffer more. Currently, in the UK, there are 6.6 beds every 100.000 population for intensive care, while the EU average is 11.5. Then the quarantine is necessary to save lives and allow a prompt restart once the crisis is over.
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