Interventions targeting air travellers early in the pandemic may delay local outbreaks of SARS-CoV-2
Samuel J Clifford, Petra Klepac, Kevin Van Zandvoort, Billy J Quilty, CMMID nCoV working group, Rosalind M Eggo, Stefan Flasche
doi: https://doi.org/10.1101/2020.02.12.20022426
Abstract
Objectives: To determine if interventions aimed at air travellers can delay establishment of a SARS-CoV-2 outbreak in a previously unaffected country. Design: Simulation study Setting: Countries with no sustained SARS-CoV-2 transmission and with no shared border with affected regions Participants: Infected air travellers Interventions: Syndromic screening at departure and/or arrival & traveller sensitisation to the COVID-2019-like symptoms with the aim to trigger rapid self-isolation and reporting on symptom onset. Main outcome measures: The achievable delay until a major local outbreak is likely to occur Results: We evaluated traveller sensitisation effectiveness in reducing the number of secondary cases of 30, 50 and 70%, and assumed either 1, 10, or 100 infected travellers per week. Early in the outbreak when only few infected travellers arrive, traveller sensitisation can delay a major outbreak in a previously unaffected region. For 50% sensitisation effectiveness, and assuming 1 infected traveller per week, we find that in 75% of simulations the outbreak is delayed by at least 11 days (97.5% of simulations: at least 7 days). The possible delay decreases rapidly for more travellers, lower effectiveness of sensitisation, higher R0 or lower heterogeneity thereof. Syndromic traveller screening at departure and/or arrival can further enhance outbreak delays. In combination with sensitisation, syndromic screening can delay an outbreak substantially longer. In 75% of simulations we find an outbreak delay of at least 111 days (97.5% of simulations: at least 23 days) for 1 infected traveller per week and at least 9 days (97.5% of simulations: at least 4 days) for 10 infected travellers per week. Conclusion: Air-traveller targeted interventions, particularly in combination, can delay local SARS-CoV-2 outbreaks in the magnitude of a few weeks to potentially even months if the number of infected travellers remains low.
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