At a time when many countries are starting to relax containment measures decided to fight against coronavirus, the fear in all minds is that the contaminations will start again, causing a “second wave“epidemic.
“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 French Prime Minister Edouard Philippe on Tuesday during the presentation of his plan to gradually de-paralyze the country from May 11.
Perverse effect of containment
Like Belgium and 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’s a “delicate ridge line“, in the words of Edouard Philippe: relieve cloistered populations and 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 thus estimates that the proportion of French people who were infected on May 11 was less than 6%.
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%).
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“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 France Inter radio.
Several modeling studies in different countries conclude a second epidemic wave “very probable“and”no earlier than the end of August“but it could also be”later in the fall, in October or November“, she adds.
Among the pessimists in the United States, a senior public health official, Robert Redfield, said he feared an episode for next winter “even more difficult than the one we 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.
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Optimism Remains
Among the optimists, Pierachille Santus, professor of pulmonology in Milan, predicts a second wave “probably smaller than the first“thanks to the maintenance of control measures, with around 30%” fewer and sick patients “in a less serious state”.
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 calm period for the summer”, hoped Monday the president of the French scientific council Jean-François Delfraissy, while fearing a “recidivism” in autumn.
If several laboratory experiments “indicate a reduction in the survival of Sars-Cov-2 at elevated temperatures”, nothing guarantees that this effect is found in the real world, however warned a group of experts consulted by the American Academies of 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 the wearing of 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 discarded 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 “have maximum screening capabilities “, to isolate positive people and to be able to “make an entourage survey” among these people, underlines Didier Pittet, head of the infection prevention and control service of the Geneva University Hospitals (HUG).
Under these conditions, “we would have a succession of small wavelets“, he explained. To achieve this objective, 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 the rate to 1 for the first time since mid-April, after falling to 0.7, prompted the authorities to call for caution.
Because there is little room for maneuver: 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 from June at 1.3.
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