The shadow of the Covid-19 “superpropagators” hovers over the finish

While the French government has just specified the next stage of decontamination, the German example shows that a risk hangs over this new phase of the health crisis: the events of “super-contamination”.

Shortly after the relative return to normal in Germany on May 6, a 100 people became infected with Covid-19 during a meeting in a church in Frankfurt. A few days later, about twenty customers at a small restaurant in Lower Saxony, celebrating their reopening, suffered the same fate. These infection centers where an individual or a small group of individuals are the source of an abnormally high number of pollutants are worrying, while European countries are organizing their gradual containment. The Germans are afraid that these “superpropagators” and these “super-contamination” eventsis behind the dreaded second wave of the epidemic.

The “super propagators” had disappeared somewhat from media lines at the height of the pandemic. Not surprisingly, when the virus spreads on a large scale, the fact that some Covid-19 carriers infect more people than the average does not change much in the overall picture. Scientifically said: this is when there are relatively few cases that “R0 with ‘super-contamination’ or without is very different”, explains Jean-Stéphane Dhersin, Deputy Scientific Director of the National Institute of Mathematical Sciences and specialist in epidemic modeling, contacted by France 24.

“Supercontaminators” and R factor

In this statement, R0 corresponds to the factor for reproduction of the virus, that is, the average number of people that will be contaminated by each carrier of Covid-19. It is the main variable to monitor the development of an epidemic, because as soon as it exceeds 1, the spread threatens to escape all control. “If R0 is greater than 1, a patient will contaminate more than one. Therefore, the epidemic will increase. If it is less than 1, patients will too little contaminate fewer people and therefore the epidemic may decrease or disappear.”declared Health Minister Olivier Véran on April 6.

It may take some “super pollution” to dramatically change the course of an epidemic during the initial phase. This is what happened in South Korea, with the famous patient # 31 who alone infected more than 100 people in February. These events of “super propagation” also explain “how the epidemic developed rapidly in the Bergamo region of Italy or what happened in Oise”, Jean-Stéphane Dhersin specifies.

This is why Europe is entering the closing phase, the multiplication of pollutants in slaughterhouses is alarming. These are typical examples of events that can restart the machine to spread the new corona virus. But there is a catch. “Supercontaminators” only act as an accelerator for an epidemic when the rest is already over 1. Below, the virus naturally disappears from the landscape as it no longer reproduces. And officially confirmed Olivier Vérana on Thursday May 28 R was less than 1 in the majority of the territory.

“Supercontaminators” and K-factor

So what the hell are the “super pollutants”? In reality, “we don’t know what R0 is at the end of the prison,” says Jean-Stéphane Dhersin. The reason is simple: this variable is calculated only outside any measure of social distance.

In order to more accurately assess the risk that the events of “super propagation” pose during the closing period, it would be necessary to know to what extent they contributed to the dynamics of the Covid-19 pandemic. It is then advisable to be interested in a new letter and go from R to … K. This second parameter, called dispersion factor, indicates the homogeneity of the contogen. In other words, it is possible to know if each carrier in an outbreak of contamination will infect approximately the same number of individuals or if there is a big difference. The lower this K (between 0 and 1), the more the majority of the spread comes from a small number of patients.

When it comes to seasonal influenza, this spread is close to 1, which means that all carriers infect about the same number of people. Scientists have also been able to confirm thatduring the 2002 Sras epidemic, K was 0.16, which is very weak and suggests that “super propagators” played an important role. For Sars-CoV-2 the mass has not yet been said. Swiss researchers, in a study still published, have assured that this figure is much higher than for SARS, which ensures that “not as closely linked to major “super-contamination” outbreaks as 2002On the contrary, a team from the London School of Hygiene and Tropical Medicine estimates that about “80% of the pollutants are due to only 10% of the carriers.” In this model, K is very low, about 0.1, which would mean that “superpropagation” events could play a critical role in the closing phase.

The features of the current coronavirus significantly complicate K. tracker’s task. “” Supercontaminators “are only classified retrospectively by epidemiological tracking,” a 2015 study explained cited by Sciences etvenir. But in the case of SARS, “the symptoms of the disease appeared very quickly, this is not necessarily the case with Covid-19”, which complicates the tracking, Jean-Stéphane Dhersin specifies.

“Superpropagators” and the Zumba factor

In the absence of security on this front, it may then be useful to take an interest in the population of “super-contaminants”. Why do some people infect more people than the average person? “This is an interesting scientific issue that remains open,” said Christopher Fraser, a researcher at the University of Oxford, interviewed by the American magazine Science.

We know which environments are favorable for the appearance of important propagation areas. These are “big gatherings, in tight places where people stay close to each other for a long time,” says Jean-Stéphane Dhersin. The nightclubs, which played a key role in the pollution of a hundred people in Seoul in early May, the overcrowded bars, which the Austrian ski resort Ischgl is considered one of the epicenter of the epidemic in Europe, where churches, like Frankfurt, are ideal candidates for being hosting “super propagation”.

On the other hand, researchers can only come up with hypotheses to understand who will turn into a “super-contaminator”. These may be individuals with weaker immune systems or those at the beginning of the disease. In both of these cases, the viral load is higher, which suggests that they may be more contagious.

Some have even speculated on the role of breathing. A person who breathes faster or has a deeper breath would be more likely to become a “super propagator,” says Science. There are really more hot spots in Zumba classes than pilates, said Gwenan Knight, a specialist in infectious diseases at Imperial College London, interviewed by Science. “Maybe quiet, slow breathing is not a risk factor while fast, strong breathing [comme lors de cours de Zumba] is, “said the researcher.

Without precise information on the importance of these events of “super-contamination” in the dynamics of the Covid-19 epidemic or about the characteristics of the people who can trigger them, it is difficult for the authorities to take this factor into account when deciding on deconfinance. But it is likely that at a time when the government has set a date for the opening of restaurant terraces, museums and other public places, there is a risk that it has in mind.