Using county-level data on COVID-19 mortality and infections, along with county-level information on the adoption of non-pharmaceutical interventions (NPIs), we examine how the speed of NPI adoption affected COVID-19 mortality in the United States. Our estimates suggest that adopting safer-at-home orders or non-essential business closures 1 day before infections double can curtail the COVID-19 death rate by 1.9%. This finding proves robust to alternative measures of NPI adoption speed, model specifications that control for testing, other NPIs, and mobility and across various samples (national, the Northeast, excluding New York, and excluding the Northeast). We also find that the adoption speed of NPIs is associated with lower infections and is unrelated to non-COVID deaths, suggesting these measures slowed contagion. Finally, NPI adoption speed appears to have been less effective in Republican counties, suggesting that political ideology might have compromised their efficacy.

我们使用有关 COVID-19 死亡率和感染的县级数据，以及有关采用非药物干预措施 (NPI) 的县级信息，研究了 NPI 采用的速度如何影响美国的 COVID-19 死亡率。我们的估计表明，在感染翻倍前 1 天采取居家更安全的命令或非必要的企业关闭可以将 COVID-19 死亡率降低 1.9%。这一发现证明对 NPI 采用速度、控制测试的模型规范、其他 NPI 和移动性以及各种样本（国家、东北部、不包括纽约和不包括东北部）的替代措施是稳健的。我们还发现，NPI 的采用速度与较低的感染率有关，与非 COVID 死亡无关，这表明这些措施减缓了传染。最后，