Update: Quarantine alone or in combination with other public health measures to control COVID‐19: a rapid review

Background

Coronavirus disease 2019 (COVID‐19) is caused by a new virus that has spread quickly throughout the world. Most infected people either experience no symptoms or suffer mild, flu‐like symptoms, but some become seriously ill, and may die.

There is no vaccine (a medicine that stops people catching a specific disease) for COVID‐19, so other ways of slowing its spread are needed. One way of controlling the disease is quarantine. This means separating healthy people from other healthy people, who may have the virus after being in close contact with an infected person, or because they have returned from an area with high infection rates. Similar recommendations include isolation (like quarantine, but for people who tested positive for COVID‐19) and physical distancing (people without symptoms keep a distance from each other).

What did we want to find out?

We wanted to find out whether and how effectively quarantine stops COVID‐19 spreading and if it prevents death. We wanted to know if it was more effective when combined with other measures, and how much it costs.

Study characteristics COVID‐19 is spreading rapidly, so we needed to answer these questions as quickly as possible. This meant we shortened some steps of the normal Cochrane Review process. Nevertheless, we are confident that these changes do not affect our overall conclusions.

We looked for studies that assessed the effect of any type of quarantine, anywhere, on the spread and severity of COVID‐19. We also looked for studies that assessed quarantine alongside other measures, such as isolation, physical distancing or school closures. COVID‐19 is a new disease, so, to find as much evidence as possible, we also looked for studies on similar viruses, such as SARS (severe acute respiratory syndrome) and MERS (Middle East respiratory syndrome).

Studies measured the number of COVID‐19, SARS or MERS cases, how many people were infected, how quickly the virus spread, how many people died, and the costs of quarantine.

Key results 

We included 51 studies. 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 model (a simulation) for predicting how events might occur over time, for people in different situations (called modelling studies). Four COVID‐19 studies observed the effects of quarantine (observational studies) on 6064 individuals in China, Greece and Singapore. Twenty‐eight COVID‐19 studies simulated outbreaks in Algeria, China, Canada, Italy, Kazakhstan, Nepal, UK, USA, Singapore, South Korea, on the cruise ship Diamond Princess, and in a general population. Four studies looked back on the effect of quarantine on 178,122 people involved in SARS and MERS outbreaks. The remaining 15 studies modelled SARS and MERS outbreaks.

The modelling studies all found that simulated quarantine measures reduce the number of people with COVID‐19 and the number of deaths. With quarantine, estimates showed a minimum reduction in the number of people with COVID‐19 of 44%, and a maximum reduction of 96%. Similarly, with quarantine, estimates of the number of deaths showed a minimum reduction of 31%, and a maximum reduction of 76%. Combining quarantine with other measures, such as closing schools or physical distancing, may be more effective at reducing the spread of COVID‐19 than quarantine alone. The SARS and MERS studies agreed with the studies on COVID‐19.

Two SARS modelling studies assessed costs. They found that the costs may be lower when quarantine measures start earlier.

Reliability of the evidence

We are uncertain about the evidence we 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.

Conclusion

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.
This review includes evidence published up to 23 June 2020.