# 15. THE R NUMBER: Filling Maracaná

To understand COVID-19, you must know the value of R0, which is the basic reproductive number. This value indicates the average number of COVID-19 cases caused by an infected person. In other words, it indicates the ability of an infected person to infect others. In the case of the influenza virus, R0 has a value of approximately one. Ebola outbreaks in Liberia and Sierra Leone have had R0 values in a range between 1.3 and 1,9 11. In the case of SARS-CoV-2, the average R0 that results from various studies is approximately three 12.

Three doesn’t seem like a very high number, but wait a minute. An R0 equal to one, like the flu, means that you give a ticket to a person to watch a game at the stadium, and that person, in turn, gives another ticket to another person. When that chain is repeated ten times, there will be ten people with free tickets. If you coordinate, you can even sit all ten together in the same row of seats. In summary, ten consecutive rounds of infections with the flu virus resulting in ten people with the flu.

Instead, look at the mess with an R0 equal to three. You give three tickets, and each of the three people to whom you have given the ticket, give tickets to three more people. When this cycle is repeated ten times, there will be 59,049 people with free tickets, and you will not fit even in Anfield (capacity for 53,394). Therefore, ten SARS-CoV-2 chain infections would produce 59,049 people with COVID-19.

Here are the numbers:

3 x 3= 9

9 x 3= 27

27 x 3=81

81 x 3= 243

243 x 3= 729

729 x 3= 2.187

2.187 x 3= 6.561

6.561 x 3= 19.683

19.683 x 3=59.049

According to FIFA, the record for attendance at a match was in Maracana, in the 1950 final between Brazil and Uruguay, with 173,850 spectators (most standing and crowded, of course). To reach that number of people infected with SARS-CoV-2, we would only need one more cycle of gifted tickets 59,049 x 3 = 177,147. They would not even fit in the current largest stadium in the world, which is the May Day Reunion, in North Korea, where 150,000 spectators can be accommodated.

With a couple more rounds we would reach thirteen cycles, and then there would not be seats for everyone in the stadium designed by artist Paul Pfeiffer, who has created a model where a million spectators could sit. Yes, you read it right. One million. The model, according to Pfeiffer, is transferable to the real world, and it has been called Vitruvian Experiments in honor of Marcus Vitrubio, who was the architect of Julius Caesar and author, before Christ was born, of the oldest known architectural treatise.

If an R0 of three now seems serious, a recent study by the Center for Disease Control (CDC) in the United States suggests that the R0of SARS-CoV-2 could reach 5,7 13. Make the numbers, but I already tell you that, giving away tickets six by six, after just seven cycles you need three stadiums like the Camp Nou (99,000 spectators) to get people in.

The R0, or value of the basic reproductive number, is calculated with mathematical models considering different variables. Therefore, its final value is also variable according to estimates. What seems evident is that the R0 of SARS-CoV-2 is above the previous coronavirus outbreaks (SARS and MERS). Those epidemics that you didn’t even know about.

Why can SARS-CoV-2 have a higher R0 than other coronaviruses? I’ll explain it to you in the next chapter, with the help of former Liverpool striker Peter Crouch.

THE BOOK, WHICH INCLUDES SCIENTIFIC REFERENCES, IS AVAILABLE WORLDWIDE, IN AMAZON.