Considerations regarding the duration of quarantine for people with possible exposure to SARS-CoV-2 infection

Given that the number of COVID-19 cases in Switzerland has been increasing, the priority for SARS-CoV-2 control strategy is to stabilise or reduce case numbers using the full range of public health and individual level prevention measures.

Reducing the duration of quarantine should only be considered if accompanied by measures that compensate for the expected increase in transmission. A nationally coordinated approach is required.

Studies should be commissioned by the cantons or the confederation to assess the effects of the duration of quarantine on SARS-CoV-2 transmission in Switzerland, including in the setting of the current test-trace-isolate-quarantine strategy, and for imported COVID-19.

Contacts of confirmed cases and returning travellers differ in the probability of having been exposed and infected and on the information available about the likely window of exposure.

In the absence of empirical data about the effectiveness of different durations of quarantine, we use mathematical modelling to explore the fraction of onward transmission that can be prevented by different quarantine strategies.

For contacts of confirmed COVID-19 cases,

• A test-and-release strategy can reduce the period of quarantine but the earlier in the quarantine period that the test is done, the lower the fraction of onward transmission that can be prevented.
• We provide estimates of the fraction of transmission prevented for different scenarios.If test-negative individuals strengthen their adherence to preventive measures after leaving quarantine, there is a modest gain in the fraction of transmission prevented for tests done early.

For returning travellers from countries with higher incidence of SARS-CoV-2 than Switzerland,

• Data from Geneva suggest that about 1 in 200 returning travellers is diagnosed with SARS-CoV-2 infection during quarantine, substantially higher than the incidence of diagnosed infection in the general population.
• The effect of quarantine duration differs according to the duration of travel.
• A single test done on arrival in Switzerland can only prevent a small fraction of the transmission, even for longer trips, because of the false-negative rate of RT-PCR early in infection.
• A test-and-release strategy can reduce the duration of quarantine. We provide estimates of the fraction of transmission prevented for different scenarios.