Following the introduction of unprecedented “stay-at-home” national policies, the COVID-19 pandemic recently started declining in Europe. Our research aims were to characterize the changepoint in the flow of the COVID-19 epidemic in each European country and to evaluate the association of the level of social distancing with the observed decline in the national epidemics. Interrupted time series analyses were conducted in 28 European countries. Social distance index was calculated based on Google Community Mobility Reports. Changepoints were estimated by threshold regression, national findings were analyzed by Poisson regression, and the effect of social distancing in mixed effects Poisson regression model. Our findings identified the most probable changepoints in 28 European countries. Before changepoint, incidence of new COVID-19 cases grew by 24% per day on average. From the changepoint, this growth rate was reduced to 0.9%, 0.3% increase, and to 0.7% and 1.7% decrease by increasing social distancing quartiles. The beneficial effect of higher social distance quartiles (i.e., turning the increase into decline) was statistically significant for the fourth quartile. Notably, many countries in lower quartiles also achieved a flat epidemic curve. In these countries, other plausible COVID-19 containment measures could contribute to controlling the first wave of the disease. The association of social distance quartiles with viral spread could also be hindered by local bottlenecks in infection control. Our results allow for moderate optimism related to the gradual lifting of social distance measures in the general population, and call for specific attention to the protection of focal micro-societies enriching high-risk elderly subjects, including nursing homes and chronic care facilities.

中文翻译：

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社会距离测度对欧洲COVID-19流行病的影响：时间序列分析中断。

在引入前所未有的“待在家里”国家政策之后，COVID-19大流行最近在欧洲开始下降。我们的研究目标是表征每个欧洲国家中COVID-19流行病的变化点，并评估社会疏远程度与所观察到的国家流行病之间的关联。在28个欧洲国家/地区进行了中断的时间序列分析。社交距离指数是根据Google社区移动性报告计算得出的。通过阈值回归估计变化点，通过泊松回归分析国家调查结果，以及在混合效应泊松回归模型中社会距离的影响。我们的发现确定了28个欧洲国家中最可能的变更点。在变更点之前，新的COVID-19病例的发病率平均每天增加24％。从变化的角度来看，通过增加社会距离四分位数，该增长率分别降低到0.9％，0.3％和0.7％和1.7％。对于第四个四分位数，较高的社会距离四分位数的有益效果（即，将增加变为下降）具有统计学意义。值得注意的是，四分位数较低的许多国家的流行曲线也很平坦。在这些国家，其他可行的COVID-19围堵措施可能有助于控制该病的第一波爆发。感染控制中的局部瓶颈也可能阻碍社交距离四分位数与病毒传播的关联。我们的结果可以使人们对逐步取消一般人群的社会距离措施抱有适度的乐观态度，