Preventing major outbreaks of COVID-19 in jails.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections are now being found in jails throughout the USA. Conditions in jails are very conducive to the transmission of SARS-CoV-2, and social distancing is impossible. Therefore, there is widespread concern that there could be major outbreaks in jails and that jails could amplify transmission of SARS-CoV-2 in surrounding communities.

Jails can house a large number of inmates; the Los Angeles County jail (the largest in the USA) houses around 20 000 inmates. However, inmates spend, on average, 2 months incarcerated. This is because inmates in jail are either awaiting trial or sentencing or have been convicted of minor offences. As a preventive measure against coronavirus disease 2019 (COVID-19) outbreaks, some jails are releasing low-risk offenders early or admitting fewer inmates, or both. It is unclear whether these interventions will be sufficient to prevent the occurrence of major outbreaks.

The within-jail basic reproduction number for SARS-CoV-2, R0 wj, can be used to determine the proportion of inmates that need to be released early, and how early they need to be released, to prevent an outbreak occurring. R0 wj is defined as the average number of secondary infections of COVID-19 that are caused by one infectious inmate during the time that they are incarcerated. If R0 wj is greater than 1, then an outbreak will occur in the jail; if R0 wj is less than 1, an outbreak will not occur. the greater the value of R0 wj, the more severe the outbreak. To prevent an outbreak from occurring, interventions need to reduce R0 wj to less than 1.

The interventions that are necessary to reduce R0 wj to 1 are shown in the figure . Inmates who are not released early are assumed to spend an average of 60 days incarcerated. Both curves show that there are multiple interventions, in terms of the proportion of inmates that are released early and how early they should be released, that would be effective in preventing an outbreak. For example, if R0 wj equals 1·1 in the absence of interventions (red line), any of the following three interventions would be effective: (1) not admitting 9% of potential inmates to the jail; (2) releasing 20% of inmates after an average of 11 days in jail; or (3) releasing all inmates after an average of 39 days in jail. If R0 wj equals 1·5 in the absence of interventions (blue line), more extreme interventions would be necessary to prevent an outbreak occurring—for example, (1) not admitting 33% of potential inmates to the jail; (2) releasing 60% of inmates after an average of 8 days in jail; or (3) releasing all inmates after an average of 16 days in jail.

Figure

The proportion of inmates that should be released early to prevent an outbreak of coronavirus disease 2019 in a jail

The mathematical expression for the R0wj of severe acute respiratory syndrome coronavirus 2, and the parameter values used to generate the graph, are provided in the appendix. R0wj=within-jail basic reproduction number.

The actual value of R0 wj in any jail is currently unknown. However, the basic reproduction number, R0, for COVID-19 epidemics in the general population is high (eg, 3·38). If R0 wj is that high, releasing low-risk offenders early and admitting fewer inmates will mitigate (to some degree) outbreaks occurring in jails—ie, reduce the number of infections and deaths. However, it is unlikely that it would be possible to prevent major outbreaks occurring.