Rapid review: how effective is quarantine to control COVID-19?
Cochrane has published an update to the Rapid Review assessing the effectiveness of quarantine during the COVID-19 pandemic.
The updated review summarises evidence available from studies that show how quarantine affects the spread of COVID-19. The studies included in the review consistently conclude that quarantine can play a role in controlling the spread of coronavirus SARS-CoV-2. While early implementation of quarantine and its combination with other public health measures helps to ensure effectiveness, key uncertainties remain as to how these measures can best be adopted and when they can be relaxed.
Currently, there are no effective medicines or vaccines available to treat or prevent COVID-19. For this reason, restrictive public health measures such as isolation, physical distancing, and quarantine have been used in a number of countries to reduce transmission of the virus. Isolation refers to the separation of people with symptoms from others, whereas quarantine is the restriction of people who have no symptoms, but who have had contact with people with confirmed or suspected infection. Quarantine can be implemented on a voluntary basis or can be legally enforced by authorities, and it may be applied at an individual, group, or community level.
This Rapid Review update was done in a short space of time as part of Cochrane’s effort to meet the need for up-to-date summaries of evidence to support decision-making in combating the effects and impact of COVID-19. Cochrane researchers used abbreviated systematic review methods to address the following questions as quickly as possible:
Is quarantine of asymptomatic individuals who were in contact with a confirmed or suspected case of COVID-19 effective to control the COVID-19 outbreak?
Are there differences in the effectiveness of quarantine in different settings?
How effective is quarantine when combined with other interventions, such as case isolation, school closures, or antiviral drugs, in reducing transmission, incidence of diseases, and death?
Is quarantine of individuals coming from a country with a declared COVID-19 outbreak effective in controlling the COVID-19 outbreak?
The authors identified 51 relevant studies - 22 more than in the first version. Thirty-two studies focused on COVID-19, 14 on SARS, three on SARS plus other viruses, and two on MERS. Most studies combined existing data from multiple sources and assumptions to create a simulation (modelling study) for predicting how events might occur over time, for people in different situations.
The authors of this review concluded that they are uncertain about the evidence found for several reasons. The observational studies on COVID-19 did not include a comparison group without quarantine. The COVID-19 studies based their models on limited data and made different assumptions about the virus (e.g. how quickly it would spread). The other studies investigated SARS and MERS so they only provide indirect evidence.
Despite limited evidence, all the studies found quarantine to be important in reducing the number of people infected and the number of deaths. Results suggest that quarantine was most effective, and cost less, when it started earlier. Combining quarantine with other prevention and control measures may have a greater effect than quarantine alone, as lead author Barbara Nussbaumer-Streit of Danube University Krems, Austria explains.
‘We published the first version of this review in April 2020. Since then 22 additional studies on quarantine for COVID-19 have become available. While the number of studies has increased significantly in a short space of time, the evidence base is still limited because most studies on COVID-19 are mathematical modelling studies that make different assumptions on important model parameters. The evidence suggests that implementation of quarantine early on in a pandemic and combining quarantine with other public health measures such as physical distancing, can help slow the spread of COVID-19. However, it is difficult to determine what combination of measures is the best to reduce the number of cases and deaths.’
