The virus eats us, the paranoia virus

An anonymous passerby waits for the green light in front of a zebra crossing. He entertains himself looking at the screen of his phone in silence, until he looks up and bluntly states "The coronavirus is going to bury us all." At that moment, the green light appears, saves the phone and as soon as you start walking you light a cigarette.

I have witnessed this scene, but the same work is represented every day throughout the world: people worried about the coronavirus while being exposed to much greater risks. You might think I'm exaggerating, but let's talk about numbers. The death toll from coronavirus has been 2770 in two months. Each one of them was a person with family and friends and his death is a real tragedy, but how many people do you think has killed tobacco in that same period? Think a figure. I already tell you that it surpasses those killed by coronaviruses, we speak of neither more nor less than about 40,000 deaths worldwide. And yet that man lit a cigarette.

For some reason, it seems that this message does not go away and that the panic spreads like a spot of oil in the sea, covering everything in its path. We are living a social phenomenon, not a rational response to the real danger of the outbreak. But we have good news, the most dangerous thing about coronavirus is the misinformation you can consume without realizing it, and for that there is a vaccine: don't believe anything.

An irrational monkey

It is true that COVID-19 is a very recent strain of coronaviruses and that much remains to be known about it, but there are things that we do have clear. We know that it is not flying through the air, but is transmitted in droplets of saliva that travel a lot of meters. We know that, therefore, the risk of more than two meters is almost null and that the masks only make sense if we are going to maintain close contact with someone allegedly infected, or if it is we who are infected. However, we find health professionals turning their backs on their medical knowledge and stealing masks from his hospital. Why this paranoia?

Humans are quite good at finding patterns, but thanks to mathematics we know that our ability to make decisions is far from optimal. In nature it did not matter so much to be the most efficient as to survive, although for that you have to be a bit “exaggerated”. Our thinking is loaded with biases that pollute the decisions we make and that, now that we do not live in the savannah, have lost much of their usefulness. We tend to overestimate the dangers when it comes to something unknown, which can be cautious, but when there are objective data that contradict our fears, these should take precedence over any fear of novelty.

The relentless bombardment of sensationalist news, the emergence of thousands of social media viewers, entrepreneurs who pretend to make a box selling false therapies and fans of conspiracy theories are the gasoline that feeds the dread that many people feel when they are named coronavirus We talk about emotions so strong and fundamental that they influence the way we see the world, causing us to seek information that reaffirms our fears and that we obviate everything else, conditioning our decision making and, in a way, pushing us to deplete stocks of masks and disinfectant gel.

Cats and influencers

Seeing the reaction of people, anyone would say that we are facing a particularly contagious and deadly virus. The media talk about its rapid expansion, pandemic and mortality that fluctuates between 2 and 4%. All this seems extremely serious, if it were not that epidemiologists do not support these claims.

It is likely that you have seen those graphs where the growth of the coronavirus shows faster and faster, as a slope that keeps getting steeper and steeper. It is also possible that you have heard that it is an exponential growth, such as when we multiply a number by two many times, that at first it grows slowly, but soon it is giving uncontrollable jumps getting lost in the infinite. This has caused a few influencers to take out paper and pen and play to be epidemiologists. Taking into account the exponential growth of which the media speak, the tweeters have predicted that the death toll will reach millions in a few months. But are they right?

The key is in R0 is what is called the number of people that a sick subject can infect before healing or dying. In this case, the R0 of the coronavirus is 2.28. More or less like the flu, less than HIV (between 2 and 5) and almost 8 times less than measles. Anyway, if we only look at this, we will see clearly the exponential growth that Twitteros predict, but do you know what grows faster than the coronavirus ?: Cats.

By twisting the concept of R0 a little we can calculate the equivalent for the proliferation of cats. Taking into account that they are fertile for 11 years (and imagining that at the same time they die), with two annual litters of 4 pups per couple, an R0 of 44 leaves and that is a very conservative calculation. In other words, another 44 are born for each cat before the first dies. It is a very approximate calculation, but sufficient for our purposes, because now we can visualize the data. Let's take an initial population of two cat pups and let one year go by, so we'll have 8 kittens. If we wait another year those 8 will have become 128, in three years 2048 and if we leave them alone ten years we will reach 500,000 million, almost as many as human beings across the planet.

However, cats have been with us for millennia and if we apply exponential growth we will find that the number becomes so huge that my computer is unable to calculate it and throws the abbreviation of "Infinity" on the console. But for us to get an idea, in just 500 years, our kingdom of cats would have reached an impossible figure to read: one followed by three hundred zeros. Given that a cat weighs 4 kilos, our herd in 500 years would be as heavy as four billion planets as Earth.

The model is quite conservative, and many statistics suggest that a cat "at full capacity" can have almost twice as many pups as we have estimated, but even then the results give real barbarities. How is it possible? Why are we not surrounded by cats?

The answer is simple: the model is incomplete. R0 is not enough to predict how a disease will spread, among other things because it varies over time. For example, cats do not reproduce unlimitedly because they depend on a finite food source, when there are too many famines begin, mortality increases and fertility decreases. Similarly, the R0 of viruses depends on having subjects to infect, which can become difficult when all the subjects around you are infected. That is why it is so important to know how the infected are distributed, in this case, concentrating on the vast majority in Hubei. Along with this, preventive measures can reduce it much more: wash your hands frequently, cough inside the elbow, stay at home if we have symptoms, etc. So we better leave the Dunning-Kruger aside and let it be expert epidemiologists who build the models that allow us to predict the spread of the outbreak.


However, there is much more obvious misinformation, such as that the mortality of the coronavirus is 2%. Mortality is calculated as the percentage of deaths due to the coronavirus divided by the total population. But 2 out of every 100 people in the affected countries have not died, it has been 2770, there must be an error. This is because 2% is not of mortality, but of "fatality", which is calculated as the percentage of deaths from coronavirus among the infected population. Now that the accounts come out, 2770 deaths among 81,322 infected gives a lethality of 3.41%. The next question is clear: how high is this lethality?

It is common to hear that its lethality is more than 30 times that of the flu, which is around 0.1%, but this measure has a trick. Almost 94% of cases are in Hubei, a place where health systems have been exceeded since the first days of the outbreak and are not being able to provide the medical coverage we have in Spain. In fact, and this is key, mortality outside Hubei is 0.7%. Only 7 out of every 1000 infected. Mainly the elderly, with chronic respiratory diseases or immunosuppression, in short: the same population at risk as with seasonal influenza, which according to the latest data from the CSIC, influenza has a randomness of 1.2% almost doubling that of the coronavirus.

There is no big lethality difference between the flu and the new coronavirus, in fact, there are countless more lethal infections to which we do not give even a tenth of the attention that coronavirus has received. The lethality of the meningococcus is 10% and the MERS outbreak reached 37%. It really all depends on which pathogen we compare it to, but it is curious to see the few people who are vaccinated against the flu and how many care to buy masks for the coronavirus

Moreover, only 5% of patients have severe symptoms, in 80% of cases they are so mild that they can be confused with fever, cough and some difficulty breathing. In fact, many people will have passed the new coronavirus without finding out, making the statistics only take into account the most serious cases and inflate the lethality of the virus. Although, if all this is true, why are so many preventive measures taken? The reason is that not all countries have our luck in terms of health quality. The arrival of the coronavirus in countries less prepared to face it or with more susceptible people could trigger a tragedy.

The danger is you

So no, the numbers do not accompany the collective feeling and, however, there may be a reason to be afraid: you. As if it were a self-fulfilling prophecy, the fear of a catastrophe triggers a series of actions that end up pushing us to that disaster that we intended to avoid. The looting of masks has left many pharmacies out of stock, making those who really need them unable to find them or, if they do, their prices have become prohibitive. Home remedies have risen and the recommendation to treat coronavirus with garlic has begun to suggest the use of cocaine, as if it were a recipe extended by Freud in the nineteenth century. As if this were not enough, misinformation is fueling racism alarmingly.

Meanwhile, it seems that we lived two parallel realities, the toilets call for calm. Either those who hold executive positions away from risk areas, such as those working in affected areas, such as the doctor and scientific disseminator Pau Mateo, which is in the zero zone of the Italian outbreak. They are clear, the greatest danger is ourselves and our irrationality.


  • Epidemiological models are too complex to make with paper and pen, especially by amateurs who do not know the necessary mathematical and biological foundations.
  • Do not buy masks unless you are or are close to the population at risk. There are people who really need them.



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