“The risk of a second wave, which would strike a weakened hospital fabric, which would impose a re-confinement, which would ruin the efforts and sacrifices made (…), is a serious risk”, warned on Tuesday the Premier French Minister Edouard Philippe, during the presentation of his plan to gradually de-paralyze the country from May 11.
Like France, several European countries, a dozen states in the United States, Australia and New Zealand have started to emerge from containment, encouraged by a slowdown in contamination and deaths.
But it is a “delicate crest line”, in the words of Edouard Philippe: to relieve cloistered populations and to restart the economy without relaunching a pandemic which has already killed more than 240,000 people.
Because, paradoxical perverse effect of confinement: if it avoided an explosion in the number of infected people, preventing the saturation of hospitals, only a small part of the population has been in contact with the virus and is therefore potentially immune.
The Institut Pasteur estimates that less than 6% of the French population will have been infected on May 11.
Even in the most affected places, this rate is around 25%, according to the first surveys on the presence of antibodies in the population carried out in New York (21.2%) or around a high school in Crépy-en- Valois, in Oise, one of the first centers of the epidemic in France (26%).
“Recurrence” in the fall?
In the absence of treatment and vaccine, the resumption of activities and movement will therefore inevitably result in a re-increase in the number of infections. But with what scale and when?
“To review the virus circulating in the French population, it will be necessary to wait several weeks, even several months”, assured the virologist Anne Goffard on the radio France Inter.
Several modeling studies in different countries conclude a second epidemic wave “very likely” and “no earlier than late August”, but it could also be “later in the fall, in October or November,” he adds. she.
Among the pessimists, in the United States, a senior public health official, Robert Redfield, said he feared for next winter an episode “even more difficult than the one we have just experienced”, due to a coincidence with the seasonal flu.
This is also the opinion of virologist Christian Drosten, adviser to the German government, who warned against a second wave more powerful than the first.
Among the optimists, Pierachille Santus, pulmonology professor in Milan, predicts a second wave “probably less than the first” thanks to the maintenance of control measures, with approximately 30% “of patients less and patients” in a less state serious”.
Others also suggest that the new coronavirus, like other respiratory viruses, may be sensitive to weather factors.
There is probably a link with heat and humidity. We expect to have a fairly peaceful period for the summer, “hoped Monday the president of the French scientific council Jean-François Delfraissy, while fearing a” recurrence “in the fall.
If several laboratory experiments “indicate a reduction in the survival of Sars-Cov-2 at high temperatures”, there is no guarantee that this effect is found in the real world, however warned a group of experts consulted by the American Academies Sciences.
“Succession of wavelets”
But other levers can be activated to keep the virus under control, mainly the pursuit of “barrier gestures” (physical distance, hand washing), supplemented by wearing a mask.
Leaving containment in France without a strong policy of barrier gestures could result in a total death toll of 200,000, against around 165,000 deaths with physical distancing and 85,000 by adding the wearing of a mask, according to a modeling carried out by the company Public Health Expertise.
Even in this case, hospital services would be saturated, unless prolonging the isolation of 75% of fragile populations, a measure ruled out in France at this stage, said the study, pending publication.
Another essential lever: breaks the transmission chains by closely monitoring the emerging foci.
Hence the importance of “having maximum screening capacities”, of isolating positive people and of being able to “do an entourage survey” among these people, underlines Didier Pittet, head of the prevention and control service of the infection of the Geneva University Hospitals (HUG).
Under these conditions, “we would have a succession of small wavelets”, he explained.
To reach this goal, the authorities have a thermometer: the virus reproduction rate, which measures the number of new people infected by each infected person.
Estimated at 3.3 without control measures, this »R0« dropped to 0.5 in France with containment, according to estimates.
The challenge is to keep it below 1 so that the number of new cases continues to decrease.
In Germany, the rebound in this rate to 1 for the first time since mid-April, after falling to 0.7, prompted authorities to call for caution.
Because the room for maneuver is narrow: with an infection rate “at 1.1, we could reach the limits of our health system in terms of beds in intensive care by October”, recently warned Chancellor Angela Merkel, adding that they would be reached in July at 1.2 and in June at 1.3.
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