Table 2

Effect of international travel measures

StudySettingStudy designModel typesEpidemiological assumptionsTravel measure(s)Outcomes investigatedScenarios of interventionEstimated effect(s)
Suspended transportation
Anzai et al31GlobalModelledPoisson regression model.Mean incubation period of 5 days.Wuhan travel restrictions.Number of exported cases.Travel restrictions effective 23 January.From 28 January to 6 February, 226 cases (95% CI 86 to 449) were prevented from being exported globally (70% reduction).
JapanModelledNegative binomial model; hazard function.R0: 1.5, 2.2 and 3.7; contract tracing: 10%, 30% or 50% of contacts isolated.Wuhan travel restrictions.Probability of a major outbreak.Presence of travel restriction and with 10%/30%/50% of contacts traced and isolated.R0 (2.2): absolute risk reduction was 7%, 12% and 20% for contract tracing levels 10%, 30% and 50%, respectively. Largest effect when R0 (1.5) and 50% of contracts traced led to 37% absolute risk reduction.
Time delay to a major outbreak.Median time delay was less than 1 day when R0=2.2–3.7, and 1–2 days when R0 is 1.5.
Chinazzi et al28GlobalModelledIndividual-based, stochastic global epidemic and mobility model.Epidemic start date 15 November–1 December 2019; R0: 2.57 (90% CI 2.37 to 2.78); Tg: 7.5 days; Td: 4.2 days; global detection of cases can be as low as 40%.
Td: 4.2 (90% CI 3.8 to 4.7).
Wuhan travel restrictions.Relative risk of case importation.Travel restrictions effective 23 January.A 77% reduction in cases imported from China to other countries in early February. Prior to 23 January, 86% of international cases originated in Wuhan, afterwards most cases came from other Chinese cities.
International travel restrictions: 59 airlines suspended or limited flights to Mainland China and several countries (USA, Russia, Australia and Italy) imposed travel restrictions.Number of internationally imported and detected cases.40%–90% overall traffic reduction to and from mainland China; transmissibility reduction in China 0%.The number of imported cases is initially reduced by 10× but returns to 170–35 detected cases a day by 1 March (40%–90% traffic reductions, respectively).
Number of internationally imported and detected cases.40%–90% overall traffic reduction to and from mainland China; transmissibility reduction in China 25%.The number of imported cases is initially reduced by 10× but returns to 26–5 detected cases a day by 1 March (40%–90% traffic reductions, respectively).
Number of internationally imported and detected cases.40%–90% overall traffic reduction to and from mainland China; transmissibility reduction in China 50%.The number of imported cases is initially dramatically reduced, epidemic growth in China delayed and number of internationally imported cases remains in single digits by 1 March.
Adiga et al34GlobalModelledLinear regression models.NSSuspension of flight routes by airlines (voluntary or mandated by travel bans).Arrival time of first case.Actual airline suspensions, based on IATA data.An increase in estimated arrival time of approximately 4–5 days. Ethiopia and Qatar observe an increase >10 days.
Wells et al32GlobalModelledMaximum likelihood approach.NSWuhan and Hubei travel restrictions.Exportation risk and exported cases.Travel restrictions were implemented in Wuhan on 23 January and Hubei on 24 January.Reduced exportation risk by 81.3% (95% CI 80.5% to 82.1%) and averted 70.5% (95% CI 68.8% to 72.0%) of exported cases by 15 February 2020.
Kucharski et al33GlobalModelledStochastic transmission dynamic model.100% of cases become symptomatic.Wuhan travel restrictions.Transmission dynamics outside of Wuhan.Travel restrictions effective 23 January.The transmission reduced by about half in the 2 weeks following introduction but does not directly test effectiveness of such measures.
Costantino et al36AustraliaModelledPoisson regression model; age-specific deterministic model.R0: 2.2; infectious period: 12.2 days; effectiveness of home quarantine: 50%; home quarantine: 14 days; excludes Diamond Princess Cruise Ship effects.Australia’s ban on flights from China coupled with home quarantine of entering travellers.Imported cases to Australia from China.Complete travel ban from 2 February to 8 March, then full lifting of ban.32, 43 and 36 infected cases every 2 weeks would be averted from 26 January onwards.
Complete travel ban from 2 February to 8 March, then partial lifting of ban for students.Similar to above.
Total cases and deaths in Australia.Complete travel ban from 2 February to 8 March, then full lifting of ban.An estimate 87% reduction in cases and deaths.
Complete travel ban from 2 February to 8 March, then partial lifting of ban for students.Similar to above.
Adekunle et al35AustraliaModelledStochastic metapopulation model.China R0: 2.63 (1 December 2019–31 January 2020) and 1.73 (afterwards).Australia’s travel ban on flights from China.Imported cases and onset of widespread transmission in Australia.Travel bans begin on 24 January.By 2 March, 79% reduction in expected cases and delayed onset of widespread transmission by 4 weeks.
Australia’s travel ban on flights from Iran, South Korea and Iran.Imported cases.Travel bans begin on 2 March.Negligible impact on imported cases or local transmission.
Linka et al37European UnionModelledMathematical deterministic SEIR model.R0: 4.62±1.32 (mean, across all states) or a range from 2.7 (Denmark) - 8.7 (Austria); latent period 2.56; infectious periods 17.82.Travel restrictions introduced in the European Union (external and some internal).Number of exposed, infectious and recovered patients by country.Restrictions were implemented on 17 March.Travel restriction slowed faster spread of the virus, especially in Central Europe, Spain and France.
Screening
Clifford et al38TheoreticalModelledNon-homogeneous Poisson process with intensity function; mathematical model.R0: 1.4–3.9; others listed in table 1.Syndromic exit/entry screening plus traveller sensitisation to self-isolate if they develop symptoms.Delay in the outbreak.Screening in the context of 1 or 10 or 100 infected travellers per week.With one infected traveller per week, the outbreak is delayed by 4 days (10 travellers/1 day).
Screening plus sensitisation in the context of 1 or 10 or 100 infected travellers per week.With one infected traveller per week, the outbreak is delayed by 8 days (10 travellers/2 days).
Mandal et al39IndiaModelledMathematical model.R0: 2, 4.Port-of-entry based screening on travellers from China to India.Time to reach 1000 cases in India.Screening of both symptomatic and asymptomatic cases is feasible.Additional detection of 90% asymptomatic individuals was required to delay the epidemic by 20 days, but unclear if this is even feasible.
Wells et al32WorldwideModelledMaximum likelihood approach,
Monte Carlo simulations.
NSSelf-identification on arrival of symptomatic travellers.Probability of identification.With only symptomatic cases were detected.Could potentially identify up to 95% of infected travellers, assuming effectiveness of the questionnaire.
Broad measures including travel restrictions
Cowling et al30Hong Kong SARObservationalTime series study.NSBorder restrictions in combination with quarantine and isolation as well as social distancing and school closures.Effective reproductive number.January through end of March in Hong Kong.Demonstrates that together the measures were effective at reducing the effective reproductive number but were not able to isolate impact of border restrictions.
  • IATA, International Air Transport Association; NS, not specified; SEIR, Susceptible, Exposed, Infectious, Recovered; Td, doubling time; Tg, generation time.