SC Connecticut News

Yale researchers have assessed the necessary quarantine duration for international travelers to prevent a rise in COVID-19 infections, finding that it varies significantly by country.

In December 2022, China lifted its stringent COVID-19 restrictions, leading to a rapid increase in infections. In response, some countries imposed travel restrictions on travelers from China to curb their own infection rates. However, a new Yale study suggests that such strict border controls may not have been necessary for many nations.

The study, published in the International Journal of Infectious Diseases, utilized national demographics from over a dozen countries, COVID-19 infection rates, and travel data to determine the optimal quarantine period required to maintain infection rates at levels similar to those under total border closure. The findings indicate that the optimal quarantine lengths differ markedly between countries, with some requiring only a few days and others benefiting from complete border closure.

“The idea behind quarantine is to keep a disease from entering your country,” said Jeffrey Townsend, Elihu Professor of Biostatistics at Yale School of Public Health and senior author of the study. “And it’s incredibly effective when used that way. But during the COVID-19 pandemic, quarantines were being used by countries that already had infection spread. That makes its effectiveness more complicated. It’s worth knowing how to best apply quarantine so you don’t unnecessarily overuse resources to implement it.”

The researchers' approach uses real-world numbers for factors like population size, infection rates, immunity levels, and traveler numbers to determine the minimum quarantine time needed to prevent international travel from significantly increasing a country's COVID-19 infection rates.

For example, Scotland required shorter quarantine times—three days—due largely to its small number of daily travelers from China (226 people). Conversely, France needed 13-day quarantines due to higher immunity and lower prevalence of COVID-19 within its population; an influx of infected travelers would substantially raise infection counts in such scenarios.

At extreme ends were countries like Singapore, South Korea, and Japan that needed no quarantine because their high prevalence of COVID-19 meant new infections would have minimal impact. On the other hand, Vietnam and Thailand required complete border closures due to their very low infection rates which could be disrupted by incoming infected travelers.

“The beauty of this model is its accessibility and broad generalizability in unique pandemic situations,” said Dinesh Bojja ’26, student researcher in Townsend’s lab and lead author of the study. “Regardless of the location, virus or stage of pandemic, policymakers can easily determine what level of quarantine to impose to protect their citizens — making it incredibly powerful as a preventative tool in future pandemic responses.”

The effectiveness of this approach hinges on accurate and timely data on infection rates provided by countries. The researchers emphasize that evidence-based decision-making leads to more effective policies that better serve public health.

“Pandemic responses are health decisions and cost decisions,” said Townsend. “This approach identifies what actions are sufficient to achieve the best health protections. Public health and pandemic preparedness offices should have this model available for advising politicians on appropriate measures.”