Effect of internationally imported cases on internal spread of COVID-19: a mathematical modelling study

December 7, 2020

Peckham, H., de Gruijter, N.M., Raine, C. et al.

Lancet Public Health

This study sought to understand the effect of international travel on the spread of COVID-19 within 162 countries. The authors used modelling to predict the proportion of cases that were imported from international travelers versus transmission within country based on the average number of cases per day in each country in the months of May and September 2020. The authors then compared what would have happened had international travel stayed at 2019 levels for those months or been at 2020 travel levels. At 2019 travel volume levels, 102 of 136 countries (95% CI: 63-129) would have experienced no more than 10% of their COVID-19 cases from international travel compared to 74 countries (95% CI: 33-114) at 2020 travel volumes. For the month of September, less than 1% of cases would have been from international travel in 44 countries (95% CI: 8-97) at 2020 travel volumes and half of these countries (n=22) had epidemic growth rates below exponential growth. The results of these models suggest that international travel will likely lead to the importation of COVID-19 cases, but strict travel restrictions may not be as beneficial in places where countries have high local incidence as international importation of cases will make up a small portion of the overall cases in a country.

Peckham, H., de Gruijter, N.M., Raine, C. et al. Male sex identified by global COVID-19 meta-analysis as a risk factor for death and ITU admission. Nat Commun 11, 6317 (2020).

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