Effectiveness of interventions targeting air travellers for delaying local outbreaks of SARS-CoV-2

Abstract

Background: We evaluated if interventions aimed at air travellers can delay local severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) community transmission in a previously unaffected country.

Methods: We simulated infected air travellers arriving into countries with no sustained SARS-CoV-2 transmission or other introduction routes from affected regions. We assessed the effectiveness of syndromic screening at departure and/or arrival and traveller sensitisation to the COVID-2019-like symptoms with the aim to trigger rapid self-isolation and reporting on symptom onset to enable contact tracing. We assumed that syndromic screening would reduce the number of infected arrivals and that traveller sensitisation reduces the average number of secondary cases. We use stochastic simulations to account for uncertainty in both arrival and secondary infections rates, and present sensitivity analyses on arrival rates of infected travellers and the effectiveness of traveller sensitisation. We report the median expected delay achievable in each scenario and an inner 50% interval.

Results: Under baseline assumptions, introducing exit and entry screening in combination with traveller sensitisation can delay a local SARS-CoV-2 outbreak by 8 days (50% interval: 3-14 days) when the rate of importation is 1 infected traveller per week at time of introduction. The additional benefit of entry screening is small if exit screening is effective: the combination of only exit screening and traveller sensitisation can delay an outbreak by 7 days (50% interval: 2-13 days). In the absence of screening, with less effective sensitisation, or a higher rate of importation, these delays shrink rapidly to <4 days.

Conclusion: Syndromic screening and traveller sensitisation in combination may have marginally delayed SARS-CoV-2 outbreaks in unaffected countries.

Keywords: Coronavirus; covid-19; public health emergency of international concern; travel screening.

Figure 1

Schematic of the air traveller intervention process. A proportion of infected travellers (red dots) will be detected through syndromic exit or entry screening (green arrows) and will immediately be isolated and not cause secondary cases (yellow dots) in the as yet unaffected destination. Travellers not identified by syndromic screening enter the destination country (red arrows), where they are provided by sensitisation information and are more likely to self-isolate and/or report their symptoms soon after onset and cause fewer secondary cases (dots that are yellow under ‘delayed contact tracing’ but grey under ‘rapid contact tracing’).

Figure 2

Complementary empirical cumulative density functions for the estimated number of days an outbreak is delayed given an intervention consisting of a combination of traveller screening and sensitisation and contact tracing. Rows correspond to different arrival rates and columns to traveller sensitisation. Comparisons are made to no contact tracing and no screening (there are no ‘No screening’ results at 0% sensitisation as this is the baseline against which comparisons are to be made)