Strategies at points of entry to reduce importation risk of COVID-19 cases and reopen travel

Abstract

Background: With more countries exiting lockdown, public health safety requires screening measures at international travel entry points that can prevent the reintroduction or importation of the severe acute respiratory syndrome-related coronavirus-2. 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 coronavirus disease-2019 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.

Keywords: Lockdown; SARS-CoV-2; air passengers; border measures; isolation; quarantine; travel restrictions.

Figure 1

(a) The sensitivity of the PCR test over time. (b) The distributions used to estimate the number of infection days from illness onset to death and (c) from infection time to illness onset. (d) The distribution used for time to admission for cases that are hospitalised in the country of origin

Figure 2

Depiction of scenarios (S1–S6) and outcomes, which are labelled and colour coded. Individuals who land or receive no testing measures in Strategy 1, 4 and 5 are displayed as (1) in dark grey. Individuals who land and are tested in Strategy 2, 3 and 6 are presented as (2) in blue and those who are tested positive and quarantined for at least 7 days are shown as (3) in red. For Strategy 3, individuals who are tested and remain quarantined until 14 days are represented as (4) in orange. For Strategy 6, individuals who are denied entry when tested upon landing are presented as (5) in pink. Dark grey routes represent active pathways on arrival and light grey signify inactive routes where no testing is conducted. A dotted line signifies the denial of entry up to that timepoint or complete denial of entry for Strategy 6. For Strategy 4 and 5, quarantine measures are in place at 7 days and 14 days, respectively, and for Strategy 2 and 3, isolation measures are in place for those who test positive. At the end time point, individuals who tested positive and have been cleared (purple), tested negative (dark blue) and are unconfirmed (green) are presented

Figure 3

(a) The estimated number of infected travellers per 100 000 arrivals from countries of origin on a logarithmic scale, (b) the differences in quarantine days between Strategy 2 (7 day isolation) and Strategy 4 (7 day quarantine), and Strategy 3 (14 day isolation) and Strategy 5 (14 day quarantine) and (c) the number of secondary cases estimated to occur as individuals are permitted entry according to the travellers’ infectious time remaining

Figure 4

The number of infection days left shown as a proportion among travellers arriving. Those who are infectious on arrival are in dark grey, and those who are not infectious yet are in light grey