Greece’s border agents last year had enough Covid tests to swab only 17 percent of people who sought to enter the country. They managed the shortage by using an AI system to flag high-risk visitors.

What’s new: Between July and November, 2020, Greece deployed a reinforcement learning system to help border agents decide which travelers to test before admitting them to the country. A recent analysis confirmed that it was more effective than other methods.

How it works: Eva, a system developed by Attikon University Hospital and the Universities of Athens, Pennsylvania, Southern California, and Thessaly, was used at all 40 of the country’s entry points.

  • Eva aimed to allocate available tests at each point of entry in a way that balanced estimated risk of infection for certain groups (based on data from immigration forms including age, sex, country of origin, and region within the country) against uncertainty in the estimation of risk. In this way, it focused on the highest-risk visitors while distributing tests more broadly.
  • The system provided a list of visitors to test. Test results came back 48 hours later.
  • The algorithm adjusted its estimates of risk and uncertainty daily based on the latest test results. In addition, it allowed officials to update the number of tests available daily.

Results: Eva identified between 1.25 and 1.45 more infected travelers than testing travelers strictly based on their country of origin. Compared to random testing, Eva identified four times more infected travelers during the peak travel season (August and September) and 1.85 times more outside the peak season. As vaccines came into use and tests became more available, one of the researchers told The Batch, Greek authorities set Eva aside. The country now simply requires every visitor to provide either proof of vaccination or a negative test.

Behind the news: Many countries, seeking to contain the spread of Covid, barred visitors based on where they came from, relying on population-level factors such as the volume of Covid cases and deaths per capita in the visitor’s home country. Since then, several studies have shown that such methods are flawed due to the medical community’s early missteps in understanding how Covid spreads.
Why it matters: The pandemic so far has taken millions of lives and livelihoods. Assuming they don’t disadvantage any group unfairly, models like this can help countries keep their borders open and while mitigating the risk of international spread.

We’re thinking: Greek authorities installed this model in a pre-existing bureaucracy that manages thousands of visitors daily. Its success offers hope for projects in fields like healthcare that interoperate with similarly complex and messy human systems.


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