That will be right at the end ? The pessimists who continue to paint the future black ? Or the optimists who see it rather in pink ? Professor Antoine Flahault remains cautious. “ I do not grant more credit to those who argue so emphatically that there will be a second wave of the epidemic to those who say the opposite in an equally categorical “, indicates the director of the Institute of global health from the university of Geneva.
” The truth is that at this stage, nobody can say what will happen in the weeks and months to come “, says professor Bruno Lina, virologist and member of the scientific board set up in mid-march by the Elysée palace.
“We are all a little screwed up “,
Then the second wave or not ? The question is of course central when France began this week, a return to a life a little less abnormal. But for the moment, no scenario does the consensus from modellers and epidemiologists. ” It is all a little screwed up “says the one two.
A few weeks ago, many feared that, given the low herd immunity, the output of the confinement is not accompanied by a rebound of the epidemic, potentially very fast. With a possible return imposed French at home, before the summer, at least in the departments still red.
However, after three weeks of déconfinement, it is as if, finally, good news came on the front of the Covid, which does not seem to recover to circulate with great intensity. “Even if we must wait another one to two weeks, the scenario of a rebound very fast from the epidemic away “, writes Mircea Sofonea, lecturer in epidemiology at the university of Montpellier.
“We must remain very cautious when talking about the history of epidemics “
But should it yet in the conclusion the end of the epidemic ? It is the belief of professor Didier Raoult, who, at the end of April, raised on YouTube the natural history of epidemics. “The epidemics start, speed up, they culminate, this is the time of maximum communicability. And diminishing, and they disappear, and we don’t know why “, moving then to the virologist marseille
“ It is necessary to remain very cautious when talking about the history of epidemics “explains, for his part, professor Renaud Piarroux, head of the department of parasitology at the hospital of the Pitié-Salpêtrière hospital. “This coronavirus, nobody knew six months ago. Therefore, do not have a certainties too, affirmed. Because in history, it has also seen outbreaks of the climb, go back down and leave again without anyone there to wait “adds this doctor, who has fought against the cholera in Haiti or the DR-Congo, and participated in the establishment of mobile teams of tracing the Covid-19 of the public Assistance-Hospitals of Paris (APHP).
A containment unpublished
This epidemic can be extinguished because it would have reached the end of its natural cycle ? Some, in any case, recall the case of the severe acute respiratory syndrome (Sars). Already a coronavirus, which emerged in late 2002 in China before it spread in some thirty countries and more than 700 people dead. Then disappear completely in July 2003.
” At the time, very efficient measures had been put in place to break the chains of contamination. But still today, we really don’t know if the epidemic is stopped thanks to these measures, or because it was the natural history of this virus “, said professor Anne-Claude Crémieux, infectious diseases physician at the hôpital Saint-Louis in Paris.
→ MAINTENANCE. Containment : “The level of anxiety of the French rose “
In fact, any attempt of comparison rests on the uniqueness of the current health situation. “Never in the history of public health, it has not seen as much of the country confining, and for eight weeks in the face of an epidemic “says dr. Nicolas Hoertel, a psychiatrist and modeler to the hospital Corentin-Celton, Issy-les-Moulineaux (Hauts-de-Seine). In France, three weeks after the déconfinement, the virus seems to be under control, but without knowing if it is really reflux, and natural and sustainable. Or if the Covid has been temporarily stopped by these eight weeks in which France is no longer out of the house.
“The social life has not resumed as before “
” In more than 50 countries in the world, containment or not, this is exactly the same dynamic that we have witnessed. We have seen the wave go up in four weeks then back down in eight weeks. And, today, in none of these countries, we do not see second wave “said professor Jean-Francois Toussaint, director of the Institute for research in biomedicine and epidemiology of sport (Irmes).
“ The containment has been very effective to slow down drastically the circulation of the virusreplica professor Bruno Lina. And if he flows down the noise today, it is also because the social life has not resumed as before. People wear masks in the transport and shops, they observe gestures barriers. Large gatherings are not allowed. “
Cross immunity and seasonality
To put in doubt the likelihood of a second wave, and others, suggest a possible cross-reactive immunity in the population. According to them, a significant proportion of individuals could be protected against the Covid-19 because they would have been infected in the past by other coronaviruses, such as managers of simple colds.
” But if this cross immunity exists and is so important, how to explain some of the contamination, massive as this has been the case on the aircraft carrier Charles de Gaulle ? “asked the professor Renaud Piarroux. On this military ship, 1 046 sailors have been infected by the Covid-19 1 700 crew members.
Another hypothesis, finally, the importance of the seasonal factor in the spread of the virus. “The arrival of the summer period could explain that the epidemic will not restart in the temperate countries of the northern hemisphere. While in some temperate countries of the southern hemisphere, such as Chile, Argentina, southern Brazil, or in south Africa, the epidemic has started its exponential phase with the beginning of the cold season “notes Antoine Flahault.
“The priority is to strengthen our ability to response to the virus “
If this seasonality were to be confirmed, we could not exclude a resumption of the epidemic in the fall, and why not every fall. “We can very well imagine that the virus to come back every year like the flu “believes Romulus Breban, a researcher at the unit of epidemiology of emerging diseases at the Pasteur Institute.
“For me, the question is not whether there will be or not a second wave, slice Antoine Flahault. Because nobody has the answer today. The priority is to strengthen our ability to response to the virus in order not to react even in emergency if this second wave occurs well. To look at what other countries have done and invent solutions other than the containment. Because it does not seem conceivable that we can stop completely new France during the winter months. “
No second wave in other countries
In China, the number of deaths daily is in continuous decline since the end of February, and almost nil since the 20 April. The number of reported cases has declined consistently since mid-February until 16 march, and then experienced a slight rebound during 15 days (from an average of 20 to 100 cases detected per day) before starting a new decline. The country declared since the end of April, less than ten cases per day.
In Italy, after having reached a peak in early April (820 deaths per day), the curve of daily deaths has been declining steadily, falling below 100 today. The number of patients detected follows the same progression, from more than 5 600 at the end of march to less than 500 today.
In Japan, much less affected than Italy or China, the dynamics follows the same logic. The number of deaths daily was close to thirty at the end of April and is now less than ten people per day. The reported cases rose from about 650 per day in mid-April, less than 45 today.