Estimating internationally imported cases during the early COVID-19 pandemic

Area of Science:

• Epidemiology
• Public Health
• Infectious Disease Modeling

Background:

• Early COVID-19 outbreak predictions relied heavily on cases from Wuhan, potentially overlooking other significant importation sources.
• International travel patterns played a crucial role in the global dissemination of COVID-19 during the initial pandemic phase.

Purpose of the Study:

• To develop and apply a novel method for estimating COVID-19 importations from multiple Chinese cities to international destinations.
• To assess the contribution of various Chinese cities, beyond Wuhan, to early international COVID-19 spread, with a focus on African nations.

Main Methods:

• Integrated daily COVID-19 prevalence data with flight passenger volume data.
• Modeled importations from 18 Chinese cities to 43 global destinations, including 26 African countries.
• Analyzed the temporal shifts in primary source cities for international COVID-19 importations.

Main Results:

• Initial importations in January were mainly from Wuhan, but shifted to other Chinese cities by mid-February, particularly for African destinations.
• An estimated 10.4 (6.2 - 27.1) COVID-19 cases were imported to the studied African destinations, with significant variations in source and magnitude.
• Approximately 90% of estimated imported cases arrived between January 17 and February 7, preceding official case detections in many regions.

Conclusions:

• Source locations for international COVID-19 importations are dynamic and can shift over time.
• Understanding these shifting source dynamics is critical for refining global disease surveillance and response strategies.
• The study underscores the importance of considering diverse origins of imported cases, especially for vulnerable regions like Africa.