Abstract
The COVID-19 epidemic was reported in the Hubei province in China in December 2019 and then spread around the world reaching the pandemic stage at the beginning of March 2020. Since then, several countries went into lockdown. Using a mechanistic-statistical formalism, we estimate the effect of the lockdown in France on the contact rate and the effective reproduction number Re of the COVID-19. We obtain a reduction by a factor 7 (Re = 0.47, 95%-CI: 0.45–0.50), compared to the estimates carried out in France at the early stage of the epidemic. We also estimate the fraction of the population that would be infected by the beginning of May, at the official date at which the lockdown should be relaxed. We find a fraction of 3.7% (95%-CI: 3.0–4.8%) of the total French population, without taking into account the number of recovered individuals before April 1st, which is not known. This proportion is seemingly too low to reach herd immunity. Thus, even if the lockdown strongly mitigated the first epidemic wave, keeping a low value of Re is crucial to avoid an uncontrolled second wave (initiated with much more infectious cases than the first wave) and to hence avoid the saturation of hospital facilities.
Highlights
COVID-19 epidemic was reported in the Hubei province in China in December 2019 and spread around the world reaching the pandemic stage at the beginning of March 2020 [1]
Official data on the number of deaths by COVID-19 since the beginning of the epidemic in France only take into account hospitalized people
Many studies focused on the estimation of the basic reproductive number R0 of the COVID-19 epidemic, based on data-driven methods and mathematical models [e.g., [4, 27]] describing the epidemic from its beginning
Summary
COVID-19 epidemic was reported in the Hubei province in China in December 2019 and spread around the world reaching the pandemic stage at the beginning of March 2020 [1]. In France, the first cases of COVID-19 were detected on January 24, and the lockdown has been set on March 17 This national lockdown means important restrictions on movement, with a mandatory home confinement except for essential journeys including food shopping, care, 1 h individual sporting activity and work when teleworking is not possible, and closing of the borders of the Schengen area. It includes closures of schools and universities as well as all non-essential public places, including shops (except for food shopping), restaurants, cafés, cinemas, and nightclubs
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