September 19, 2021

the decline of the epidemic continues, but at a slower pace

The weather for Covid-19 is good. The decrease in all indicators of the epidemic is confirmed for the fifth week in a row. Hospitalization levels reached those of mid-May 2020, at the time of the first deconfinement; the number of people in critical care fell below the threshold of 3,000 people on the 1stis June. Deaths of patients hospitalized for Covid-19 continued to decline and fell below 100 per day.

However, it is still too early to say that the epidemic is behind us. The reproduction rate rose slightly, from 0.75 to 0.8, and even reached 0.88 for admissions to intensive care units. “This recovery began at the beginning of May, which corresponds to the resumption of secondary school, knowing that there may also be an effect, admittedly more limited, of the primary”, analysis Mircea Sofonea, lecturer in epidemiology and evolution of infectious diseases at the University of Montpellier.

Regarding a possible “terracing effect” that the first stage of deconfinement led to fear, on May 19, no resumption of contamination is to be observed for the moment, but it will still be necessary to wait a week before being able to measure precisely the consequences of these reopenings. “We do not expect these outside activities to restart the epidemic, because there was a much larger effect of the third lockdown than expected”, emphasizes the researcher.

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This sharp decrease in the epidemic had not been anticipated by most epidemiological models. Regarding that of his modeling team, Mircea Sofonea explains that it had been calibrated on the model of the first two confinements, where the reproduction rate fell sharply in the first phase and then rose again. But in the case of the third confinement, Easter week ultimately proved to be more conducive to the circulation of the virus than those that followed.

“This shows that the models still have things to improve”, acknowledges Mircea Sofonea, while recalling that they are based on assumptions and that they are in no way predictions. For the researcher, this unexpected decrease confirms that the closure of schools has broken the chains of transmission.

Immunization protection

For his part, Jean-Stéphane Dhersin, deputy director of the National Institute of Mathematical Sciences and their interactions of the CNRS, underlines that the models have poorly integrated the public holidays of May, interpreted differently according to the experts in the calculation of the incidence rate. Because each time it is a question of compensating for the low detection rates of these exceptional days, either by applying the data of a normal day to them, or by using them. “Forgetting”. “We had a blurry view of the descent, certainly slower than that of the second wave, but constant, admits the mathematician. There was also a problem of identifiability of the causes, several causes leading to the same effects. “

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