Data_Sheet_1_Impact of Lockdown on the Epidemic Dynamics of COVID-19 in France.ZIP

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.

2019年12月，中国湖北省首次报告新型冠状病毒肺炎（COVID-19）疫情，随后疫情在全球蔓延，并于2020年3月初升级为大流行疫情。自此之后，多国相继实施封控措施。本研究采用机制统计学形式化方法，评估法国封控措施对新型冠状病毒肺炎接触率与有效再生数（effective reproduction number, Re）的影响。相较于疫情早期法国境内的估算结果，我们发现相关指标降低至原水平的1/7（有效再生数Re=0.47，95%置信区间：0.45–0.50）。我们同时估算了截至官方宣布解除封控的5月初，法国累计感染人口的占比。在未纳入4月1日前未知的康复人数的情况下，我们估算该占比为法国总人口的3.7%（95%置信区间：3.0%–4.8%）。该比例似乎过低，不足以实现群体免疫（herd immunity）。因此，即便封控措施有效抑制了首轮疫情浪潮，维持有效再生数Re处于低位仍至关重要：此举可避免出现失控的第二轮疫情（其初始感染病例的传染性远高于首轮），进而防止医疗资源出现挤兑。