Epidemic disease can spread during mass gatherings. We assessed the impact on the local-area trajectory of the COVID-19 epidemic of a type of mass gathering about which comprehensive data were available. Here, we examined five types of political events in 2020 and 2021: the US primary elections; the US Senate special election in Georgia; the gubernatorial elections in New Jersey and Virginia; Donald Trump's political rallies; and the Black Lives Matter protests. Our study period encompassed over 700 such mass gatherings during multiple phases of the pandemic. We used data from the 48 contiguous states, representing 3,119 counties, and we implemented a novel extension of a recently developed non-parametric, generalized difference-in-difference estimator with a (high-quality) matching procedure for panel data to estimate the average effect of the gatherings on local mortality and other outcomes. There were no statistically significant increases in cases, deaths, or a measure of epidemic transmissibility (Rt) in a 40-day period following large-scale political activities. We estimated small and statistically insignificant effects, corresponding to an average difference of -0.0567 deaths (95% CI = -0.319, 0.162), and 8.275 cases (95% CI = -1.383, 20.7), on each day, for counties that held mass gatherings for political expression compared to matched control counties. In sum, there is no statistical evidence of a material increase in local COVID-19 deaths, cases, or transmissibility after mass gatherings for political expression during the first two years of the pandemic in the USA. This may relate to the specific manner in which such activities are typically conducted.

翻译：疫情期间，大规模聚集可能加速传染病传播。本研究基于可获取的全面数据，评估了某类大规模聚集活动对当地COVID-19疫情演变轨迹的影响。我们分析了2020至2021年间五类政治事件：美国初选、佐治亚州参议员特别选举、新泽西与弗吉尼亚州长选举、唐纳德·特朗普政治集会以及"黑人的命也是命"抗议活动。研究覆盖疫情期间多个阶段，共计700余场此类集会。采用美国本土48州3119个县的数据，通过将近期发展的非参数广义双重差分估计量与（高质量）面板数据匹配程序进行创新性拓展，估算大规模聚集对当地死亡率及其他结果变量的平均效应。结果显示，在大规模政治活动后40天内，各县病例数、死亡数及疫情传播力指标（Rt值）均未出现统计学显著增长。我们估算出微小且无统计显著性的效应值：相比匹配对照组，举办政治表达类聚集活动的县每日平均死亡差异为-0.0567例（95%置信区间：-0.319至0.162），病例差异为8.275例（95%置信区间：-1.383至20.7）。综上，在疫情暴发前两年内，美国本土政治表达类聚集活动并未对当地COVID-19死亡数、病例数或传播力产生统计学可证实的实质性影响。这一现象可能与这类活动的典型开展方式有关。