key: cord-0893099-4pvjc4un authors: Dickens, Borame L; Koo, Joel R; Lim, Jue Tao; Sun, Haoyang; Clapham, Hannah E; Wilder-Smith, Annelies; Cook, Alex R title: Strategies at points of entry to reduce importation risk of COVID-19 cases and re-open travel date: 2020-08-25 journal: J Travel Med DOI: 10.1093/jtm/taaa141 sha: 5e7d95a3c7e00fc5928b774ff0749341925122c8 doc_id: 893099 cord_uid: 4pvjc4un BACKGROUND: With more countries exiting lockdown, public health safety requires screening measures at international travel entry points which can prevent the reintroduction or importation of the SARS-CoV-2 virus. Here, we estimate the number of cases captured, quarantining days averted and secondary cases expected to occur with screening interventions. METHODS: To estimate active case exportation risk from 153 countries with recorded COVID-19 cases and deaths, we created a simple data-driven framework to calculate the number of infectious and upcoming infectious individuals out of 100 000 000 potential travellers from each country, and assessed six importation risk reduction strategies; Strategy 1 (S1) has no screening on entry, S2 tests all travellers and isolates test positives where those who test negative at 7 days are permitted entry, S3 the equivalent but for a 14 day period, S4 quarantines all travellers for 7 days where all are subsequently permitted entry, S5 the equivalent for 14 days and S6 the testing of all travellers and prevention of entry for those who test positive. RESULTS: The average reduction in case importation across countries relative to S1 is 90.2% for S2, 91.7% for S3, 55.4% for S4, 91.2% for S5 and 77.2% for S6. An average of 79.6% of infected travellers are infectious upon arrival. For the top 100 exporting countries, an 88.2% average reduction in secondary cases is expected through S2 with the 7-day isolation of test positives, increasing to 92.1% for S3 for 14-day isolation. A substantially smaller reduction of 30.0% is expected for 7-day all traveller quarantining, increasing to 84.3% for 14-day all traveller quarantining. CONCLUSIONS: The testing and isolation of test positives should be implemented provided good testing practices are in place. If testing is not feasible, quarantining for a minimum of 14 days is recommended with strict adherence measures in place. With more countries exiting lockdown, public health safety requires screening measures at international travel entry points which can prevent the reintroduction or importation of the SARS-CoV-2 virus. Here, we estimate the number of cases captured, quarantining days averted and secondary cases expected to occur with screening interventions. To estimate active case exportation risk from 153 countries with recorded COVID-19 cases and deaths, we created a simple data-driven framework to calculate the number of infectious and upcoming infectious individuals out of 100 000 000 potential travellers from each country, and assessed six importation risk reduction strategies; Strategy 1 (S1) has no screening on entry, S2 tests all travellers and isolates test positives where those who test negative at 7 days are permitted entry, S3 the equivalent but for a 14 day period, S4 quarantines all travellers for 7 days where all are subsequently permitted entry, S5 the equivalent for 14 days and S6 the testing of all travellers and prevention of entry for those who test positive. The average reduction in case importation across countries relative to S1 is 90.2% for S2, We simulate arrivals from a country of origin, , calculating risks per 100 000 travellers in 1000 simulations to accommodate uncertain travel volumes. The conditional distribution of importation at different stages of infection is obtained from these 100 000 000 simulated travellers. Those who were infected but not yet recovered were extracted for further modelling. The amount of secondary transmission over their infected lifespan was then apportioned into transmission potential before arrival, during quarantine or isolation if any, and in the community. Quarantine and isolation measures were assumed to take place in a designated healthcare facility or centre where transmission risk is reduced to negligible levels, or at home with strict adherence where any family members present are also expected to follow the same measures. We assumed travellers were administered a PCR test upon arrival and estimated the likelihood of identifying each positive infection using a binomial distribution where the probability of detection was a function of their time from symptom onset using data from Xiao et al. 31 (Figure 1a ). PCR sensitivity was assumed to be 85% for two days pre-symptom onset, similar to sensitivity two days post onset, and infections were undetectable at any earlier point during the incubation period. Asymptomatic individuals were assumed to follow the same detection profile as symptomatic individuals. For a country of origin and travel date assumed to be 23 rd July 2020, we simulated the incidence of infection among 100 000 000 travellers that (1) occurred prior to , (2) were not admitted to hospital, and (3) did not become non-infectious prior to . To obtain estimates of the daily number of infections in , we utilised daily incidence and death data being published by JHU CSSE 32 across 153 countries from 22nd Jan 2020 to 6th August 2020. To estimate condition (1), we first simulated the time of infection ( ) for each individual reported to have died at time in country C using estimates from Linton et al. 18 With ongoing concerns of false negative rates in PCR testing 35, 36 , strained test kit availability 37 , and lack of trained manpower and laboratories 38 The use of immunity passports 19, 40 or similar certification could help mitigate such ethical issues and relieve resource use for testing and quarantining should the traveller be confirmed to have been previously positive, or a vaccine become available. Their use however requires a better understanding of the dynamics of waning immunity and test sensitivity over time. Lastly, country-specific estimates will require continued updating where the same analysis at different time points (Appendix 3; equivalent of Figure 3 carried out on June 28 th ) will show countries moving ranks according to their ongoing reported case numbers and deaths, although the relative efficacies of the strategies explored are expected to remain largely the same. Those who are infectious on arrival are in dark grey, and those who are not infectious yet are in light grey. Ebola virus outbreak in North Kivu and Ituri provinces, Democratic Republic of Congo, and the potential for further transmission through commercial air travel Zika in travellers 1947-2017: a systematic review The rise in travel-associated measles infections-GeoSentinel Imported dengue in Spain: a nationwide analysis with predictive time series analyses Could Ross River Virus be the next Zika? Zika in Angola and India Potential Zika virus spread within and beyond India Estimated global exportations of Zika virus infections via travellers from Brazil from 2014 to Association between air travel and importation of chikungunya into the USA Correlation between travellers departing from Wuhan before the Spring Festival and subsequent spread of COVID-19 to all provinces in China Nowcasting and forecasting the potential domestic and international spread of the 2019-nCoV outbreak originating in Wuhan, China: a modelling study The positive impact of lockdown in Wuhan on containing the COVID-19 outbreak in China The effect of travel restrictions on the spread of the 2019 novel coronavirus (COVID-19) outbreak Impact of international travel and border control measures on the global spread of the novel 2019 coronavirus outbreak The effectiveness of full and partial travel bans against COVID-19 spread in Australia for travellers from China during and after the epidemic peak in China Effectiveness of travel restrictions in the rapid containment of human influenza: a systematic review Travel restrictions and infectious disease outbreaks Re-starting Travel in the Era of COVID-19: Preparing Anew COVID-19 Immunity Passport to Ease Travel Restrictions Physical distancing interventions and incidence of coronavirus disease 2019: natural experiment in 149 countries Potential for global spread of a novel coronavirus from China High prevalence of SARS-CoV-2 infection in repatriation flights to Greece from three European countries High proportion of asymptomatic and presymptomatic COVID-19 infections in air passengers to Brunei Household secondary attack rate of COVID-19 and associated determinants in Guangzhou, China: a retrospective cohort study Prevalence of Asymptomatic SARS-CoV-2 Infection: A Narrative Review Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship Risk perceptions of COVID-19 around the world Lockdown timing and efficacy in controlling COVID-19 using mobile phone tracking Imperial College COVID-19 Response Team et al. Estimating the effects of nonpharmaceutical interventions on COVID-19 in Europe Preparedness and vulnerability of African countries against importations of COVID-19: a modelling study Profile of RT-PCR for SARS-CoV-2: a preliminary study from 56 COVID-19 patients An interactive web-based dashboard to track COVID-19 in real time Estimating the infection and case fatality ratio for coronavirus disease (COVID-19) using age-adjusted data from the outbreak on the Diamond Princess cruise ship Incubation Period and Other Epidemiological Characteristics of Novel Coronavirus Infections with Right Truncation: A Statistical Analysis of Publicly Available Case Data Variation in False-Negative Rate of Reverse Transcriptase Polymerase Chain Reaction-Based SARS Tests by Time Since Exposure Interpreting a covid-19 test result CDC's Diagnostic Test for COVID-19 Only and Supplies Charting the challenges behind the testing of COVID-19 in developing countries: Nepal as a case study