Contract Tracing: Why virus alert apps had limited success

Human contact tracers were struggling to keep up with spiking virus caseloads, and the trillion-dollar rival companies — whose systems run 99% of the world’s smartphones — had the potential to quickly and automatically alert far more people. Soon Austria, Switzerland and other nations introduced virus apps based on the Apple-Google software, as did some two dozen American states, including Alabama and Virginia. To date, the apps have been downloaded more than 90 million times, according to an analysis by Sensor Tower, an app research firm. But some researchers say the companies’ product and policy choices limited the system’s usefulness, raising questions about the power of Big Tech to set global standards for public health tools. 

Computer scientists have reported accuracy problems with the Bluetooth technology used to detect proximity between smartphones. Some users have complained of failed notifications. And there is little rigorous research to date on whether the apps’ potential to accurately alert people of virus exposures outweighs potential drawbacks — like falsely warning unexposed people, over-testing or failing to detect users exposed to the virus. 

“It is still an open question whether or not these apps are assisting in real contact tracing, are simply a distraction, or whether they might even cause problems,” Stephen Farrell and Doug Leith, computer science researchers at Trinity College in Dublin, wrote in a report in April on Ireland’s virus alert app. 

In the United States, some public health officials and researchers said the apps had demonstrated modest but important benefits. In Colorado, more than 28,000 people have used the technology to notify contacts of possible virus exposures. In California, which introduced a virus-tracking app called CA Notify in December, about 65,000 people have used the system to alert other app users, the state said. 

“Exposure notification technology has shown success,” said Dr. Christopher Longhurst, the chief information officer of UC San Diego Health, which manages California’s app. “Whether it’s hundreds of lives saved or dozens or a handful, if we save lives, that’s a big deal.” In a joint statement, Apple and Google said: “We’re proud to collaborate with public health authorities and provide a resource — which many millions of people around the world have enabled — that has helped protect public health.” 

Based in part on ideas developed by Singapore and by academics, Apple and Google’s system incorporated privacy protections that gave health agencies an alternative to more invasive apps. Unlike virus-tracing apps that continuously track users’ whereabouts, the Apple and Google software relies on Bluetooth signals, which can estimate the distance between smartphones without needing to know people’s locations. And it uses rotating ID codes — not real names — to log app users who come into close contact for 15 minutes or more. Some health agencies predicted last year that the tech would be able to notify users of virus exposures faster than human contact tracers. Others said they hoped the apps could warn commuters who sat next to an infected stranger on a bus, train or plane — at-risk people whom contact tracers would not typically be able to identify. 

Some limitations emerged even before the apps were released. For one thing, some researchers note, exposure notification software inherently excludes certain vulnerable populations, such as elderly people who cannot afford smartphones. For another thing, they say, the apps may send out false alarms because the system is not set up to incorporate mitigation factors like whether users are vaccinated, wearing masks or sitting outside.