For the first time, researchers have determined how long a sufficient travel quarantine needs to be to prevent an increase in transmission of COVID-19 within a country. In many cases, researchers found a period of three days or shorter—far less than the prevailing standard of 14 days—is sufficient to prevent travel from increasing incidence of the highly infectious disease.
The study, led by researchers at the Yale School of Public Health and published in the journal The Lancet Regional Health—Europe, examined the pandemic in 26 European countries as of November, and found that for most origin-destination country pairs, a three-day or shorter quarantine—accompanied by RT-PCR or antigen testing on exit—suffices.
The researchers also found that for nearly half of the origin-destination country pairs analyzed, travel could be permitted in the absence of quarantine and testing. For the majority of pairs requiring controls, a short quarantine with testing could be as effective as a complete travel ban, said lead study author Jeffrey Townsend, Ph.D., the Elihu Professor of Biostatistics at the Yale School of Public Health and professor of ecology and evolutionary biology at Yale.
“Fourteen-day quarantines are typically far beyond what is necessary to achieve the equivalent of a complete travel ban,” Townsend said. “We show that travel quarantine and testing strategies can effectively mitigate importation and onward transmission within a country. Identifying sufficient strategies can allow countries to permit travel to and from other countries without risking increases in infection rates.”
The findings, Townsend said, can provide guidance for travel policy for all phases of the pandemic. Early in a pandemic, when there is no disease in the destination country, the theory indicates a long quarantine that will wholly prevent introduction of disease. Late in a pandemic, when disease and variants are widespread, the recommendation is for much shorter quarantines that ensure transmission rates do not increase due to travel.
Once community transmission is ongoing, the long-term epidemic trend within the destination country is more likely to be determined by other disease control measures, such as contact tracing, vaccination and non-pharmaceutical interventions. Together, travel quarantine and other related control measures can mitigate the risk of transmission between countries, appropriately limiting the threat posed by the COVID-19 variants.
The practice of quarantine, Townsend noted, began during the 14th century to protect coastal cities from plague epidemics. Ships arriving in Venice from infected ports were required to sit at anchor for 40 days before landing. The practice is one of the one of the oldest public health measures ever devised.
“It amazes me that before this research there was no theory developed to quantify its appropriate use when disease prevalence at the destination was non-zero,” Townsend said. “We provide an easy-to-use tool for its calculation—enabling its application any country interested in preventing increased disease associated with travel.”
The study was funded in part by easyJet, an economy airline based in Europe and which serves a host of European destinations.
Townsend was joined by researchers from the Center for Infectious Disease Modeling and Analysis at the Yale School of Public Health as well as by scientists from the University of Maryland School of Medicine, University of Florida and York University in Canada.