## Analyzing corona reproduction number

#### WE ARE STILL IN THE MIDDLE OF THE CORONA CRISIS AND THE REPRODUCTION NUMBER IS EVERYTHING

#### Corona Insights | 30-11-2020

*VISUALISING THE REPRODUCTION NUMBER GIVES KEY INSIGHTS IN HOW A VIRUS SPREADS AMONG SO MANY*

Definition (wiki): “*The effective reproduction number Re is used, usually written as Rt, or the average number of new infections caused by a single infected individual at time t in the partially susceptible population.*

*”*

Considering one person infected, let’s imagine this person can infect 2 people. After one step we are going to have 2 infected people. the second step the two people infected are going to infect two people more, we end up having 4 infected.

We can calculate till 10 steps, then 1024 people are infected.

Calculating until 20 steps and the below graph will show the total number of people infected.

More than a million infected in only 20 steps! So far we have seen that every person can infect 2 other people, or the average number of new infections caused by a single infected individual is 2, or in other words Rt = 2.

Lets now consider the Rt = 1.2 and we see the graph below

At step 20 there are a bit more than 38 new infected. **Rt** = 1.3 instead.

We can see by the above graph how important is the value of the **Rt** number.

Even with small changes, after 20 steps we can have more than a million infected when the **Rt** is equal to 2, instead 38 when the **Rt** is 1.2

**What is positive about this?**

Let’s consider a situation where the **Rt** = 0.8.

After 20 steps 0.01 new people are infected! Every step we need to multiply the new infected to a number less than 1, so after 20 steps we are going to end up with a number way lower than 1, almost 0.

Let’s now consider three **Rt** values = 1.1, 1.2, and 1.3 (in the graph R1, R2, R3) at the same time, and let’s focus on the differences.

In order to understand the three curves we need to read the graph vertically

When **R****t** grown also the variation of the **Rt** itself become more intensive. In the left graph above we see the **Rt** at step 14 and on the right graph the **Rt** at step 16. Going from **R****t** 1.1 to 1.2 there is little variation, but variations of **R****t** from 1.2 to 1.3 are way wider.

**W****hat this can teach us****?**

Our behavior allows us to variate the **Rt** number. Each of us affects the **Rt** number and its variation. If we keep the number of **Rt** below 1 the health system won’t have any more stress and our life can go back to normal**. ****A****ll of us count in the fight against this pandemic****.**