NUMBERS THAT COUNT.
During an epidemic, one number in particular matters a lot: it is called the net reproduction rate, and is denoted by R0 (in English, basic reproduction number).
It is the number of individuals who, on average, are infected by a single infected patient.
It is therefore clear that the higher the R0, the worse the epidemic will be, in terms of total infected individuals and the rapid spread of the virus.
But what can we do to decrease R0?
Let's see it together. We call B the number of daily contacts of an infected individual leading to new infections, and C the average period of time (in days) during which an infected individual is contagious.
By definition, we have:
R0 = B X C
That is, the average number of individuals infected by an infected patient is equal to the average number of infectious contacts per day for the number of days the patient is infectious.
At this point, it is easy to understand that, to decrease R0, and therefore slow down or block the epidemic, we must:
1. decrease B, ie decrease the number of daily contacts of each potentially infectious individual
2. decrease C, that is decrease the number of days in which an infected individual can infect others
The first step involves quarantining all those who are potentially infected.
- If "potentially infected" is equivalent to symptomatic, of all those who manifest symptoms compatible with the infection;
- If on the other hand, as in the case of the SARS-Cov2 coronavirus, there is a suspicion that even asymptomatic individuals may be carriers of the virus and contagious, then only quarantine on a geographical basis and proximity to certainly infected individuals remains.
Quarantine affects the number of contacts; to decrease B, that is the number of daily contacts that lead to contagion, we can also make it more difficult for an "effective contact" by the virus, following those few indications that the ministry and WHO have given (sneezing in the hollow of the elbow, washing thoroughly hands etc.), using health aids such as masks (for potentially infected subjects) and protection for health workers or in any case implicated in containment (suits and masks).
The second point implies the strict isolation of infected patients (and therefore certainly contagious); obviously, since it will rarely be isolated from the first day of their contagiousness, it is only possible to decrease C, never completely reset it.
Acting on B and C, i.e. using health care devices appropriately and following WHO warnings, but above all implementing quarantine and isolation, can bring the value of R0, i.e. the average number of individuals infected by each infected subject, below of 1; which, although not with immediate effect, eliminates the epidemic.
Panic, disorder, bad coordination and poor collaboration of citizens are all elements which, on the other hand, lead to an increase in the B number in particular; in fact, when they are afraid, they engage in hoarding behavior (for example by decreasing the availability of health facilities where they would be needed) and, if the containment measures are not implemented in a controlled and orderly manner, they tend to have more contacts with each other than should (especially among family members, but also to get the necessary in the absence of clear plans and indications).
Trust in our institutions, doctors and the national health system helps to coordinate the necessary measures, and therefore to effectively decrease B and C.
Knowing R0, B and C helps to understand the reason for the containment measures and the restrictions imposed, to reason calmly and to organize what is best needed in the area.
It's all here, in the simplicity of two numbers, the secret to fighting a virus for which no drugs or vaccines are yet available.
