"The epidemic is advancing and our room for maneuver is shrinking"

Could we expect the worsening of the Covid-19 epidemic? With such a dynamic, how will it evolve in the coming weeks? What measures should be put in place to flatten the curve of this second wave? Epidemiologist and biostatistician at the École des Hautes Études en Santé Publique, Pascal Crépey sheds light on these questions.

The Conversation: Has the epidemic worsened more sharply than expected over the past 10 days?

Pascal Crepey: Not really. Currently we are on the dynamic predicted by the models since the first curfew measures were taken in mid-October. The real surprise rather arose at the beginning of October: the number of reproductions suddenly increased.

(editor's note: also called "R effective", the reproduction number is an estimate, over the last 7 days, of the average number of individuals infected by an infected person).

To understand what happened, we have to go back a bit, to this summer, or even before. The epidemic remained under control after the March containment. But from mid-July, it was observed that the number of reproduction of the epidemic rose again above the epidemic threshold, that is to say above 1. In other words, the epidemic started again, very slowly, a phase of growth. This was the consequence of the resumption of our social activities. When we analyze the activity and mobility data for July and compare them with those for the month of May, we see that at the start of summer, the population had largely resumed its “pre- COVID-19 ”.

At the start of the school year, in September, the big unknown was whether people would adopt a behavior more similar to that of May-June, or whether the summer "slack" would continue, in which case the increase would increase. continue, and would eventually result in hospitalizations and deaths.

With hindsight, we see that what happened then turned out to be a sort of "mix" between these two situations: during the month of September, the number of reproductions of the epidemic fell slightly, but without however, return to pre-July levels. During this period, there was a kind of stagnation of the epidemic. The virus was still largely present, there were hospitalizations, but the dynamics were relatively stable.

This situation continued until early October and the onset of inclement weather, which roughly coincided with the arrival of Storm Alex in early October. This period marked the end of the Indian summer that we had been living until then. Rain, wind and cold forced people to spend more time indoors again, to ventilate their living spaces less, which resulted in an increase in contamination, then hospitalizations.

The increase in the number of reproductions, currently around 1,5 based on hospitalization figures, has put an end to the illusion of autumnal control of the epidemic. She reminded us that there is a seasonal factor, which had also been observed during the austral winter (which corresponds to our summer). Australia, for example, which had managed to contain the epidemic well, had nevertheless suffered a second wave. Unfortunately, this is what we are going through.

For two or three weeks, the situation has deteriorated, but without additional surprise: the daily numbers of new contaminations, hospitalizations, or intensive care admissions correspond to what was expected.

TC: At this rate, what are the models predicting for the next few weeks?

PC: Let us first underline that the projections we make are not predictions: the idea is to take the necessary measures so that they do not come true!

If we stay on the current dynamic, we arrive at the number of beds occupied in intensive care in excess of 10, or even approaching 000 beds, during the month of January. It would be less brutal than in March, because it would be slower to occur, but it would not be sustainable anyway.

Especially since, even if we succeed in having the 12 resuscitation beds promised during the first wave, they would not be enough: some of these beds would necessarily be occupied by patients who have undergone heavy scheduled operations, and by those who would have been victims of accidents, of the road or others. In March, confinement made it possible to limit these additional occupations, in particular because the number of road accidents was almost zero. As it stands, all the efforts that make it possible to reduce the number of reproductions of the virus (wearing a mask, social distancing, etc.) and therefore the contaminations are not sufficient to absorb the surplus caused by this second wave.

But of course, this projection of a dynamic that would saturate the hospital system in January does not take into account measures such as the curfew, and those that will follow. So there is still hope.

TC: What must be done to succeed, once again, in bending the curve?

PC: We have different means of action at our disposal. The first and most direct way is to limit contact between people. Indeed, it is through these contacts that the virus is spread, especially if they are done without a mask and in closed spaces. The fewer these contacts, the less chance there is of infecting others or of being contaminated. This means of action is directly accessible to all, no need to wait for it to be imposed on us.

The second element concerns the limitation of secondary cases, in other words the system of identification of positive people and the tracing of their contacts. If we want to avoid a maximum of propagation chains, this system must be very reactive.

The problem is that with the increase in cases, this system will become less and less efficient. Indeed, each time a new case is detected, the person must be called, questioned about all the risky contacts that he / she may have had, then that these contacts, either on average 2 or 3 per person, are at their turn called to tell them to isolate themselves and be tested. When we see that we are today at more than 50 identified cases per day (perhaps 000 real cases), you can imagine that the time and human resources required are becoming extremely substantial.

The solution is to automate this work. This is the purpose of the application "TousAntiCovid". Once people who have had symptoms and got tested have been confirmed to be positive, they just have to scan a QR code in the app and all of their contacts who have also downloaded it are notified. that they have potentially been infected, and therefore must self-isolate and get tested. Unfortunately, today this application has only been downloaded by 4 million people out of 50 million French people equipped with a mobile phone ...

Regarding the curfew measures, it is unfortunately still too early to assess them: we will only be able to start estimating the effect of the first curfews put in place in Île-de-France and in 8 metropolises in the next 5 to 10 days.

However, we have every reason to believe that there will be an impact. The question that remains open is: will it be enough to break the momentum and bend the curve? This is not at all certain for the moment, which is why we are preparing for stronger measures. In particular, we can fear that social contacts have shifted: people will go for drinks earlier. This is a bit like what we saw when the bars were closed: we met up with each other, which limited the effectiveness of the measure.

TC: And if that is not enough, what measures would you consider important to put in place?

PC: For me, the first measure to be put in place is not one per se: the French should realize that they do not need to wait for government measures to come to pass. up to them to reduce their physical, if not social, interactions.

This awareness is important, because we are on a crest line: if the measures are not understood, they risk not being well respected, and people will seek to circumvent them.

Secondly, there would be a real interest in, if not imposing, at least very strongly encouraging teleworking. This not only has the advantage of protecting teleworkers, but also those who, for one reason or another, cannot telework. Indeed, if part of the workforce is teleworking, there are fewer people in the workplace, which limits the number of potential contacts. Last element: teleworking results in less use of public transport, which also limits the risk of contamination. It is a good complement to wearing a mask in transport, because it does not reduce the risk of contamination to zero.

TC: We have been talking a lot about (re) confinement in recent days, some are wondering about the closure of schools… What to think?

PC: It is not certain that closing schools will change the dynamics of the epidemic much. Indeed, studies so far have shown that children tend to transmit the virus less than adolescents or adults. Middle school and high school students are potentially more transmitters than children, but perhaps also more capable of respecting barrier gestures, at least during their lessons. In the event of confinement, the question of distance education in colleges and high schools could arise.

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Regarding containment, the situation is very complicated. One thing is clear: theoretically, the earlier a containment is applied, the more effective it is. But the real question is not when to apply it; rather, we must ask ourselves whether containment is really necessary. The problem is that to answer this question it is necessary to have been able to observe the effect of curfews.

Unfortunately, this effect will not be visible for several more days. However, during this time, the clock is ticking, the epidemic is advancing, and our room for maneuver is reduced. Some regions are already in a situation of hospital tension, which requires action to be taken. Politicians will therefore have to decide without necessarily having all the information available, because it does not yet exist.

Moreover, what worries me when we talk about re-containment, is above all that people can say to themselves "let's take advantage of it before being confined again" ... The consequences of such a relaxation would in fact have an influence. very harmful to the course of the epidemic.

My main hope is that the French react intelligently to the danger, seeing the degradation taking place before our eyes: that they apply barrier measures more and more strongly, limit their contacts, use the TousAntiCovid application ... These are rational choices to be made if we want to fight effectively against the epidemic.

Pascal Crepey, Professor, Department of Quantitative Methods in Public Health (METIS), EA 7449 REPERES, School of Advanced Studies in Public Health (EHESP)

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.

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