INTERVIEW
While the second phase of deconfinement is launched, Prime Minister Edouard Philippe welcomed Thursday the good health results against the Covid-19. "Today, all the indicators are green," he said. Before clarifying: "This does not mean that the virus no longer circulates. It is still present in varying degrees throughout the territory. But its speed of spread is, at this stage, under control". Seasonality, contamination, immunity of populations, Vincent Enouf, deputy director of the national reference center for respiratory viruses of the Pasteur Institute, gives an update on Europe 1 on Sars-CoV-2.
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Can a virus completely die out?
If the epidemic is not over in France, Vincent Enouf nevertheless notes a drop in certain indicators concerning the circulation of the virus, particularly in terms of patients in the emergency room. "We will also see that at the laboratory level: there will be less detection of the virus, and this is what we are currently observing," he adds. "We observe that out of a hundred samples, depending on the region, we have four or five positive detections. All these indicators show that the virus is circulating less and that the containment has really worked"
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Notes of hope which should not however lead to a slackening of vigilance, since we do not know if the virus can be completely eradicated, explains Vincent Enouf. "What we have to do is confine ourselves to the very beginning of the epidemic, as we see with the different clusters that exist in France. For the moment, they are all circumscribed, so it works well", he recalls. "We really have an adapted surveillance system".
Can Sars-CoV-2 become seasonal?
Again, the signs should be interpreted with caution. "It is a virus that can become seasonal, for the moment we see a decrease in detections and we can very well imagine saying that in summer the virus could be less present", evokes Vincent Enouf, while recalling that 'it can always be contracted, and new outbreaks may appear. If the virus were to become seasonal, it points to an additional difficulty. "We would eventually have this virus, the influenza viruses and all the other respiratory viruses as we see every year."
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"We are going to monitor the month of June, if we see an increase in indicators. But we can say nothing, consider nothing flagrant today about the veracity of a second wave or not. In any case, we can and we prepare, have one ", tempers Vincent Enouf. "This is all the work that is done in the laboratories, the services. If we have a lull this summer, it would be good, it would allow to reserve, to prepare, to see what went wrong, so to be even better if a second wave arrives. "
How can a virus die?
Once infected with a virus, the human body defends itself with the help of the immune system. "From the moment the immune system takes over, you will have a drop in fever in a few days, and then the body will take over. If you have had muscle pain, all of this will go into effect. order, "said the deputy director of the national reference center for respiratory viruses at the Pasteur Institute.
But a virus only lives by its host, infecting living cells. "He uses cell reproduction mechanisms to live, so if he has no living cells on hand, he dies. So if we cut, by wearing masks, washing our hands and taking all the measures that exist today, the virus will be unable to infect, to find living cells and therefore it will be able to die out. This is how we break the spread, as long as we do not have effective vaccines that would prepare our immune system and prepare us for all infections, "says Vincent Enouf.
Certain hypotheses evoked the heat to eradicate the virus, thus justifying a stop of the epidemic in summer. "We can say that the heat is not good for the virus," said Vincent Enouf. In laboratories, viruses are also stored at a temperature between -20 and -80 degrees. "If you currently have a virus on a metal support in full sun, it will not survive. The sun, the heat is not a factor which allows a good diffusion of the virus", adds the assistant director. "But we observe it in countries where it is hot, because the virus circulates via humans," he recalls.
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Can cross immunity protect us before the vaccine arrives?
The race for vaccines, launched between different countries, will only yield results in a few months. Especially since today, says Vinent Enouf, there are no vaccines against other forms of coronavirus like SARS or MERS. As a ray of hope, some studies have been raising the possibility of "cross immunity" for the past few weeks. A common immune reaction to Sars-CoV-2 (which causes Covid-19) and other winter coronaviruses already in circulation and responsible for certain colds.
"There are" human "coronaviruses, which are responsible for colds. They are more or less close to Sars-CoV-2, responsible for Covid-19 and one could imagine, explain, that some people are protected because they have were infected, we were all more or less infected, by these seasonal coronaviruses ", summarizes Vincent Enouf.
There are four so-called "human" seasonal coronavirus strains: 229E, NL63, OC43, HKU1, responsible for 20% of colds according to FuturaSanté . "We could imagine that the antibodies produced during these infections partially protect us against this new coronavirus. But all that is assumed, it must currently be verified", nuances the assistant director.