Covid-19: should we really worry about the contamination records in the world?

It is a figure that can at first destabilize, when we imagined the coronavirus epidemic losing ground on the planet, after six months of existence. On Saturday, WHO recorded a record increase in the number of infections worldwide: in 24 hours, 212,326 cases were added to those already existing.

These increases in infections are far from being fairly distributed around the globe. If countries call out, such as Morocco and its peak of 700 new infections on Sunday, it is mainly states with large populations that focus attention, such as the United States (50,000 cases in 24 hours Saturday), Brazil (42,000 case), India (22,000 new infections) or South Africa (10,000 infections on Saturday).

The case of Spain, which had to reconfigure two areas locally, due to a resurgence of cases (450 new cases on Saturday) cannot be compared to that of these high density countries and is less worrying. “The situation in Europe has nothing to do with the United States or India. We are no longer in a wide and uncontrolled circulation of the virus. The problem is therefore more linked to clusters, especially in professional circles, ”reassures Pascal Crépey, epidemiologist and research professor at EHESP.

"We only see the tip of the iceberg"

He reminds us that we must first take the data on contamination, coming from the reports of the health authorities in each country, with tweezers. "We can have a little more confidence in the data from the United States, which has a fairly efficient information system, than in Brazilian or Indian data, where it is always difficult to have reliable figures. This means that many infections may have passed under the radar, especially in India, where the health system is particularly fragile.

"The difficult access to care means that we only see the tip of the iceberg and it is difficult to assess the size of the submerged part", also supports the specialist. Difficult therefore, with the only data linked to the new contaminations to draw any report on the future of the epidemic. Especially since these figures are very often correlated with a massification of tests within the population, as explained in our two graphs below.

In India and the United States, between May 13 and June 30, the number of tests carried out and contaminations declared followed a fairly similar upward trend. Clearly, the more we search, the more we find.

“As we observe the epidemic at all times, we find cases. It continues its path, its natural history: it is identical whatever the country, with an exponential rise, reaching a peak and then it descends ", decrypts Laurent Toubiana, epidemiologist, researcher at Inserm and director of Irsan (Research Institute for the Valorization of Health Data), which rejects the term "outbreak" of contamination.

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He hammers it, the mortality rate "is the most reliable indicator", to determine the progress of the epidemic. However, if we compare the contamination and mortality curves of the countries which are currently experiencing a remarkable increase in cases (India, United States, Morocco, Mexico, Brazil, South Africa, etc.), almost none follows. "The incidence of mortality is falling, the increasing number of Covid cases does not result in deaths," summarizes Laurent Toubiana.

A demographic explanation?

How, then, to explain that if the virus continues to circulate, it does not cause more deaths? The answer may well be demographic. “Wherever the virus circulates in an uncontrolled manner, in India, in South Africa, also in the Maghreb - even if the number of cases reported is small -, we have a relatively young population. When in Europe 15% of the population is over 60 years old, in West Africa it is around 5% ”, underlines the epidemiologist Pascal Crépey. He continues: "It is likely that the burden of the epidemic will be lower in these countries than in those with an older population, who are more likely to report serious forms of Covid. "

His counterpart Laurent Toubiana, puts forward another hypothesis, for India in particular, which will have to be verified. “These inhabitants are already exposed to multiple viruses and probably equivalent viruses. It is possible that the proximity to them could have immunized a large part of the population. "

In this context, the situation in the United States, where 16% of the inhabitants are over 65 years old and where obesity - another risk factor facing coronavirus - affects a large number of people, is surprising. The country has the highest number of deaths, nearly 130,000, but its share of deaths, in relation to the number of cases detected, continues to decline.

Towards new reconfigurations?

As the borders begin to reopen, this increase in contamination in highly populated countries, where it is not only a case of concentrated in clusters like in Europe, must continue to be observed carefully, in order to avoid let the situation get out of hand. "The high population density in large cities makes the spread of the virus easier and more dangerous," insists epidemiologist Pascal Crépey. However, the situation has been worrying in Brazil and the United States for a while now. "

He deplores that the authorities of these two countries "have not seen fit to apply strong measures to break the epidemic dynamic". In Brazil, the wearing of the mask was further relaxed on Monday and many critics are targeting deconfinitions deemed premature in some American states. In the case of India, it could especially be a poor preparation for deconfinement, which prevented a real control of the virus. Now there is only one solution: "The population will have to reduce its contacts to reduce the risk of spread," argues Pascal Crépey.

Smaller-scale reconfigurations, such as those initiated in Spain, Germany or China, are, according to him, the best solution "to have maximum impact, at least locally, on the dynamics of the virus".

If no solution is found, the epidemic may still increase in these densely populated countries, until it reaches “40 or 50% of the infected population”. "But inevitably, it will stagnate at some point, then slow down. People will take preventive measures on their own. Their behavior will adapt and the risk of infection situations will decrease, ”concludes the researcher.