Background

Residents of prisons have experienced disproportionate COVID-19-related health harms. To control outbreaks, many prisons in the USA restricted in-person activities, which are now resuming even as viral variants proliferate. This study aims to use mathematical modelling to assess the risks and harms of COVID-19 outbreaks in prisons under a range of policies, including resumption of activities.

Methods

We obtained daily resident-level data for all California state prisons from Jan 1, 2020, to May 15, 2021, describing prison layouts, housing status, sociodemographic and health characteristics, participation in activities, and COVID-19 testing, infection, and vaccination status. We developed a transmission-dynamic stochastic microsimulation parameterised by the California data and published literature. After an initial infection is introduced to a prison, the model evaluates the effect of various policy scenarios on infections and hospitalisations over 200 days. Scenarios vary by vaccine coverage, baseline immunity (0%, 25%, or 50%), resumption of activities, and use of non-pharmaceutical interventions (NPIs) that reduce transmission by 75%. We simulated five prison types that differ by residential layout and demographics, and estimated outcomes with and without repeated infection introductions over the 200 days.

Findings

If a viral variant is introduced into a prison that has resumed pre-2020 contact levels, has moderate vaccine coverage (ranging from 36% to 76% among residents, dependent on age, with 40% coverage for staff), and has no baseline immunity, 23–74% of residents are expected to be infected over 200 days. High vaccination coverage (90%) coupled with NPIs reduces cumulative infections to 2–54%. Even in prisons with low room occupancies (ie, no more than two occupants) and low levels of cumulative infections (ie, <10%), hospitalisation risks are substantial when these prisons house medically vulnerable populations. Risks of large outbreaks (>20% of residents infected) are substantially higher if infections are repeatedly introduced.

Interpretation

Balancing benefits of resuming activities against risks of outbreaks presents challenging trade-offs. After achieving high vaccine coverage, prisons with mostly one-to-two-person cells that have higher baseline immunity from previous outbreaks can resume in-person activities with low risk of a widespread new outbreak, provided they maintain widespread NPIs, continue testing, and take measures to protect the medically vulnerable.

Funding

Horowitz Family Foundation, National Institute on Drug Abuse, Centers for Disease Control and Prevention, National Science Foundation, Open Society Foundation, Advanced Micro Devices.

中文翻译：

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美国监狱中 COVID-19 变种的爆发：疫苗接种和重新开放政策的数学模型分析

 背景

监狱居民遭受了与 COVID-19 相关的不成比例的健康伤害。为了控制疫情，美国许多监狱限制了面对面的活动，尽管病毒变种仍在扩散，但这些活动现在仍在恢复。本研究旨在利用数学模型来评估在一系列政策（包括恢复活动）下，监狱中 COVID-19 疫情爆发的风险和危害。

 方法

我们获取了 2020 年 1 月 1 日至 2021 年 5 月 15 日期间所有加州州立监狱的每日居民级别数据，描述了监狱布局、住房状况、社会人口和健康特征、活动参与情况以及 COVID-19 检测、感染和疫苗接种地位。我们开发了一种由加州数据和已发表文献参数化的传输动态随机微观模拟。在监狱首次出现感染后，该模型会评估 200 天内各种政策情景对感染和住院治疗的影响。情况因疫苗覆盖率、基线免疫力（0%、25% 或 50%）、活动恢复以及使用可将传播减少 75% 的非药物干预措施 (NPI) 而异。我们模拟了五种因住宅布局和人口统计而异的监狱类型，并估计了 200 天内重复引入和不引入感染的结果。

 发现

如果病毒变种被引入已恢复 2020 年前接触水平、疫苗覆盖率中等（居民中疫苗覆盖率从 36% 到 76% 不等，取决于年龄，工作人员覆盖率 40%）且没有基线免疫力的监狱，预计 23-74% 的居民将在 200 天内受到感染。高疫苗接种覆盖率 (90%) 加上 NPI 将累积感染率降低至 2-54%。即使在房间占用率较低（即不超过两名居住者）和累积感染水平较低（即<10%）的监狱中，当这些监狱关押着医疗弱势群体时，住院风险也很大。如果感染反复发生，大规模爆发的风险（>20%的居民被感染）会大大增加。

 解释

平衡恢复活动的好处和疫情爆发的风险是一个具有挑战性的权衡。在实现高疫苗覆盖率后，监狱大多是一到两人的牢房，对之前的疫情具有较高的基线免疫力，只要维持广泛的 NPI、继续检测和采取措施保护医疗弱势群体。

 资金

霍洛维茨家庭基金会、国家药物滥用研究所、疾病控制与预防中心、国家科学基金会、开放社会基金会、Advanced Micro Devices。