Assessing the risk of COVID-19 importation and the effect of quarantine

Arino, J.; Bajeux, N.; Portet, S.; Watmough, J.

## Objectives During the early stage of COVID-19 spread, many governments and regional jurisdictions put in place travel restrictions and imposed quarantine after arrivals in an effort to slow down or stop the importation of cases. At the same time, they implemented non-pharmaceutical interventions (NPI) to curtail local spread. We assess the risk of importation of COVID-19 in locations that are at that point without infection or where local chains of transmission have extinguished, and evaluate the role of quarantine in this risk. ## Methods A stochastic $SLIAR$ epidemic model is used. The effect of the rate, size, and nature of importations is studied and compared to that of NPI on the risk of importation-induced local transmission chains. The effect of quarantine on the rate of importations is assessed, as well as its efficacy as a function of its duration. ## Results The rate of importations plays a critical role in determining the risk that case importations lead to local transmission chains, more so than local transmission characteristics, i.e., strength of NPI. The latter influences the severity of the outbreaks. Quarantine after arrival in a location is an efficacious way to reduce the rate of importations. ## Conclusions Locations that see no or low level local transmission should ensure that the rate of importations remains low. A high level of compliance with post-arrival quarantine followed by testing achieves this objective with less of an impact than travel restrictions or bans.