With the start of the COVID-19 pandemic, most countries closed their borders to international travelers early this year to prevent the importation of infected persons and community spread. Many international borders remain closed or severely restricted with quarantine measures to break the chain of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The virus has infected nearly 39 million people in almost all countries around the world.
Australian scientist Jessica Liebig from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), along with fellow researchers at the Queensland University of Technology and the University of New South Wales, studied the risks involved in re-opening the international borders for travelers to Australia. Their study titled, “Should international borders re-open? The impact of travel restrictions on COVID-19 importation risk,” is published on the preprint server medRxiv*.
In less than three months, the SARS CoV-2 spread to over 100 countries via international travel. A pandemic was declared by the World Health Organization (WHO) on 11th March 2020. The authors write that this prompted many nations to deny entry to international travelers.
The researchers added that this ban and restriction on international travel has lead to severe economic consequences. This economic loss, they wrote, could be quantified, but other parameters such as unemployment and societal effects have not been studied. They explained that two factors determine the expected number of COVID-19 importations into a country. These are:
- Incoming traveler volumes
- Incidence rates of the disease in source countries
Estimated daily COVID-19 importations. Model estimates that a total of 6,003 COVID-19 cases were importations into Australia between 1st January and 30th May 2020, considering the current travel restrictions (solid line). Without any travel restrictions a total of 48,715 cases would have been imported during the same time period (dashed line). The shaded are indicated the 95% confidence interval of our estimations that was obtained by averaging over 100 model runs.
Scenario in Australia
Australia is an island country, and most of the incoming international travel thus is via air. The researchers wrote that the first case was detected on 25th January 2020, and one week following that, partial border closures came into effect. Soon the number of cases started to soar until more severe restrictions on international travel came into place.
Comparison of importations by citizens/residents and visitors before and after the implementation of travel bans. The stacked bar chart shows the estimated number of importations by Australian residents and citizens before (dark blue) and after (dark green) the date of the travel ban. The light blue and light green bars show the estimated importations by visitors before and after the date of the travel ban, respectively.
Travel restrictions from Iran, South Korea, and Italy came into place on the 1st, 5th, and 11th of March 2020, respectively. All foreign travelers were banned from entering Australia since 20th March 2020.
In Australia, wrote the researchers, “border control” collects all information regarding individuals who enter into the nation, and this is published in an anonymous database. For this study, the team collected passenger volumes that would have come into the nation if there were no travel bans. They used a mathematical model called “seasonal auto-regressive integrated moving average (SARIMA) models.” They also gathered the incidence of the cases of COVID-19 using the information on the website of the European Centre for Disease Prevention and Control (ECDC).
Estimated percentage reduction of imported COVID-19 cases. The estimated cumulative number of importations by Australian citizens/residents (dashed curve) and visitors (solid curve), assuming no travel bans are implemented. The vertical dashed line indicates the date when the cumulative number of visitor importations reached one. The corresponding label shows the expected percentage reduction in the total number of importations over the studied period if a travel ban had been implemented on the same day. The solid vertical line indicates the implementation date of the actual travel ban and the corresponding percentage reduction in imported cases.
The team developed a comprehensive framework to model daily COVID-19 importations considering different levels of international travel restrictions. Each of these levels corresponded with the importation of cases and the incidence of new cases. Finally, they calculated and assessed the efficacy of the travel bans implemented by the Australian government.
Estimating the traveler volumes where first, it was assumed that there were no travel restrictions. This was based on incoming traveler data based on five-year history - January 2015 to December 2019. Then it was speculated based on the travel restrictions that the Australian government had implemented in the COVID-19 situation. They studied the effects of the travel restrictions (or none) between 1st January and 30th June 2020.
The results showed that international travel bans in Australia reduced the importations of COVID-19 cases into the country by 87.68 percent (ranging between 83.39 to 91.35 percent) between January and June 2020. Overall results of the study were:
- With the travel restrictions, Australia could lower COVID-19 importations from China by 94.45 percent (ranging between 91.77 and 96.32 percent) during the study period
- 1,938 fewer cases were imported from China
- During February, 19.57 percent of the expected number of Australian citizens/residents returned from China, they noted
- COVID-19 importations from Iran fell by 32.81 percent (14 new cases imported) since restrictions from that country came into place on 1st March
- COVID-19 importations from South Korea fell by 94.41 percent since restrictions from that country came into place on 5th March. Overall, 433 fewer cases were imported from South Korea.
- 5.49 percent of Australian citizens or residents returned to Australia during March.
- COVID-19 importations from Italy fell by 77.9 percent since restrictions from that country came into place on 5th March. Overall, 994 fewer cases were imported from Italy.
- Between 21st March and 30th, April between 15 and 22 cases a day were imported.
- Between May and June, the average cases drop was three cases a day.
- The largest proportion of imported COVID-19 cases came from the United Kingdom (1,579 cases on average)
- The second-largest source was the United States of America, with 957 cases on average.
Conclusions and implications
This study showed that case importation rates due to foreign travel into Australia and how things would be if there were no travel restrictions. The researchers wrote in conclusion, “Authorities may consider the presented information when planning a phased re-opening of international borders.”