Prisons and custodial settings are part of a comprehensive response to COVID-19.

Prisons are epicentres for infectious diseases because of the higher background prevalence of infection, the higher levels of risk factors for infection, the unavoidable close contact in often overcrowded, poorly ventilated, and unsanitary facilities, and the poor access to health-care services relative to that in community settings. Infections can be transmitted between prisoners, staff and visitors, between prisons through transfers and staff cross-deployment, and to and from the community. As such, prisons and other custodial settings are an integral part of the public health response to coronavirus disease 2019 (COVID-19).

One of the first documented influenza outbreaks in prison occurred in San Quentin prison in California, USA, during the 1918 influenza pandemic. In three separate instances, infection was introduced by a newly received prisoner, and a single transfer to another prison resulted in an outbreak there. Isolation was central to containment. More recently, prison influenza outbreaks have been described in the USA, Canada, Australia, Taiwan, and Thailand.3, 4 We are unaware of any published reports of influenza outbreaks in youth detention or immigration detention centres, although modelling suggests that outbreaks would progress similarly in these settings. Since early 2020, COVID-19 outbreaks have been documented worldwide, including Iran, where 70 000 prisoners have been released in an effort to reduce in-custody transmission.

Prisons concentrate individuals who are susceptible to infection and those with a higher risk of complications. COVID-19 has an increased mortality in older people and in those with chronic diseases or immunosuppression. Notably, multimorbidity is normative among people in prison, often with earlier onset and greater severity than in the general population, and prison populations are ageing in many countries. Furthermore, inadequate investment in prison health, substantial overcrowding in some prison settings, and rigid security processess have the potential to delay diagnosis and treatment.

As such, COVID-19 outbreaks in custodial settings are of importance for public health, for at least two reasons: first, that explosive outbreaks in these settings have the potential to overwhelm prison health-care services and place additional demands on overburdened specialist facilities in the community; and second, that, with an estimated 30 million people released from custody each year globally, prisons are a vector for community transmission that will disproportionately impact marginalised communities.

What must be done to mitigate the impact of large outbreaks of COVID-19 in prisons? The public health importance of prison responses to influenza outbreaks has been recognised in the USA, where the Centers for Disease Control and Prevention have developed a checklist for pandemic influenza preparedness in correctional settings. WHO has also issued prison-specific guidance for responding to COVID-19 (panel ).

Joint planning

Include prison health and correctional authorities in the overall public health response, rather than permitting them to plan and operate in isolation.

Risk management

Design and implement adequate systems for limiting importation and exportation of cases from or to the community, and transmission and spread within prisons.

Prevention and control

Develop protocols for entry screening, personal protection measures, social distancing, environmental cleaning and disinfection, and restriction of movement, including limitation of transfers and access for non-essential staff and visitors.

Treatment

Explicitly and transparently align prison health systems with the wider health and emergency planning systems, including transfer protocols for patients requiring specialised care. Isolate cases and contacts if required to control the spread of infection in prisons. However, special consideration of the potentially serious mental health effects of isolation in these settings is essential.10, 11 In high-income countries, maintaining isolation without depriving incarcerated people of human contact might be possible.

Information sharing

Close collaboration between health and justice ministries should be established to ensure continuity of information, which is a crucial component of an effective, coordinated, whole-of-government response. Governance of prison health by a ministry of health, rather than a ministry of justice or similar, is likely to facilitate timely information sharing.

Prison health is public health by definition. Despite this and the very porous borders between prisons and communities, prisons are often excluded or treated as separate from public health efforts. The fast spread of COVID-19 will, like most epidemics, disproportionately affect the most disadvantaged people. Therefore, to mitigate the effects of prison outbreaks on tertiary health-care facilities and reduce morbidity and mortality among society's most marginalised, it is crucial that prisons, youth detention centres, and immigration detention centres are embedded within the broader public health response.