How Many Flu Are a Coronavirus Outbreak: The Debate Over Comparing Two Diseases So Different (and So Similar)

As the coronavirus continues to spread around the world and words like "COVID", "SARS" or "R0" are introduced into everyday language, the debate about how we are communicating everything that surrounds the epidemic is also growing. There is no shortage of advocates that we are living in the midst of exaggerated collective hysteria, nor voices that consider that underestimating the virus is a huge mistake. The best example of this succession of controversies is in something that is constantly repeated: does it really make sense to compare the coronavirus with the flu?

We ourselves, a few weeks ago, wondered why everyone was talking about the coronavirus if it only seems to be one more "flu", but the truth is that, from the outset, comparing a new and relatively unknown virus with another so studied as flu is risky. Especially during the first months, when our knowledge of the coronavirus was still superficial. For this reason, now that we are learning more about the subject and the social debate is deepening, we have wondered if we are really facing another flu.

How are the two diseases similar (and how are they not)?


Symptoms It is true that the symptoms (set of symptoms and manifestations of a disease) of both viruses are similar. Above all, in the early stages of the disease we speak of a picture compatible with acute respiratory infection of any severity or a fever with no known focus. Also in both cases, the infection can lead to pneumonia (an infection that inflames the alveolar spaces of the lungs) and, if the evolution continues negative, in a respiratory distress syndrome (and sepsis).

Mortality Being aware that in this type of diseases it is very difficult to have accurate calculations (both due to the difficulty in identifying all cases, and the variability of rates according to numerous factors), we can say that, in the case of influenza, Mortality normally ranges between 0.04-0.1%. If we look at swine flu, the figures are somewhat higher (reaching 0.2%). Very far, in any case, from viruses such as SARS 2003, which reached 10%. In the case of SARS-2, the current one, the maximum ranges would place mortality between 0.7-3.5%. Although, most likely today according to epidemiological models, it is above 2.2%

Infectivity Not only does it appear to be more deadly, it also appears to be more contagious. As in the previous case, the variability depending on the circumstances is very high. However, we can say that seasonal flu has an R0 of 1.3, while SARS-2 would be between 1.4-2.5.

Incubation Period Based on the data we have so far, the average incubation period for SARS-2 appears to be slightly longer than for influenza (3-7 days for one versus 1-4 for the other). Of course, the protocols (based on other coronaviruses) continue to set the reference of 14 days and there are documented cases in which incubation lasts up to a month. However, this is normal: incubation periods in all diseases are statistical estimates.

So is the comparison relevant?


Or put another way, how can we assess whether the comparison between the flu and the coronavirus makes sense? The truth is that it is complicated. This is a somewhat different example of the "sorites paradox"; that is, to what extent can imprecision and vagueness be useful things? And the answer can not be more than a huge and sounded "depends". Basically, as Delia Graff Fara defended more than two decades ago, we must be aware that concepts and comparatives change (and are articulated) around our objectives.

There are many things that this epidemic has (or may have) in common with the flu. For example, the flu is a huge annual public health problem, and the possibility of this virus becoming something similar is on the table. In the same way, there are many others in which it could not be more different and in which comparing it with the flu only helps to confuse even more.

Finally, there are cases (most) in which the positive and the negative overlap. The usual occurrence of comparing deaths from one disease to another can help avoid collective hysteria, but also make hygiene and control measures feel unnecessary. After all, no matter how high the death toll from flu is, vaccination rates leave much to be desired. What doesn't make sense is to use the comparison thoughtlessly.

The "soccer fields" of epidemiology

Thomas Serer

However, the flu issue goes beyond this coronavirus epidemic. Over the years, we've seen how many illnesses compare to the flu. The closest case, without a doubt, is that of Ebola. And, in a sense it is understandable, human beings are relatively bad at thinking abstract and general processes.

Therefore, in the press, it is very common to see how the size of football fields is used to report on the dimension of things. Common and curious because, to tell the truth, very few people know what a soccer field really measures. It is also easy to come across "a gigantic iceberg [...] 22 times the size of Manhattan" or another "the size of La Rioja". They are heuristic, inaccurate but functional ways of dimensioning phenomena.

For this reason, when we try to measure the size of an epidemic, we resort to the epidemic that we have "at hand", that of the flu. The problem is that, compared to the flu, almost every illness we can think of is "better." It is a recurring epidemic that kills many thousands of people each year. One that we have normalized due to impotence, but that if it happened again it would generate a complete disaster. In this sense, buying flu epidemics can be understandable, but most of the time it is hardly justifiable.

Update for the preparation of the article we have used data from the WHO (influenza and coronavirus), the SVGE and the National Academy of Sciences

Image | Chris Liverani

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