Last week, Apple and Google announced an alliance to bolster what’s known as “contact tracing,” a crucial step to both controlling the pandemic in the short term and eventually reopening the economy. The plan involves using smartphones to identify and warn people who have come in contact with anyone infected with the coronavirus, while preserving individual privacy.

Apple and Google said they would introduce new features that would allow smartphones to identify other nearby devices. Those contacts would be recorded anonymously and temporarily using a standard data-sharing structure by contact tracing apps. If a user of a device later reported through an app that they had been diagnosed with the coronavirus, anyone with a recorded contact with that device would receive an alert that they may have been exposed so they can self-isolate and be alert for symptoms of infection, helping prevent further spread.

“Everything they’ve [announced] looks like it will be compatible with our ideas,” says Dana Lewis, cofounder of the contact tracing project CoEpi, and a founding member of the Temporary Contact Number Coalition, a group of a half-dozen contact tracing projects worldwide.

Since the early days of the coronavirus outbreak, a variety of U.S. nonprofit and academic projects have been trying to leverage smartphones to make contact tracing more widespread and automated. Those include efforts by researchers at Stanford University and the Massachusetts Institute of Technology, as well as those at nonprofits. Most have been testing early versions of contact tracing apps using the same basic system that will soon become standard in iOS and Android devices.

One major problem solved by Apple and Google’s initiative is improving the ability of phones to communicate with each other using Bluetooth, a short-range wireless data standard.

“Bluetooth is very, very clunky, and doesn’t work very well between phones,” says Ramesh Raskar of MIT’s SafePaths contact tracing team. “The fact that Apple and Google stepped up made everybody’s life easier.”

Google and Apple have said that their technology will only be usable by government-designated health authorities, in part to reduce the risk of false infection reports by users. CoEpi, SafePaths, and Stanford-based Covid Watch all say they are in discussions with a variety of state and national governments to help develop apps.

Those apps would be able to communicate with each other using the underlying Google-Apple data system. That’s crucial, according to Tina White, a Stanford machine-learning researcher and executive director of Covid Watch. “If you have multiple competing systems you’ll have interactions that aren’t caught…that’s really bad.”

But in contrast to monitoring systems that are used in China, agencies using the Google-Apple system will lack access to information about the location or identity of individual users. The system simply doesn’t generate or transmit that data, according to White.

“We were really trying to fight against the centralized version of this,” she says, because it would create additional privacy risk, including potentially exposing sensitive medical information.

White says the Apple-Google announcement has slowed the push in the U.S. for a centralized infection database, which the White House had reportedly considered. The anonymous system adopted by Apple and Google was first publicly described by Scott Leibrand, another cofounder of the CoEpi project, and James Petrie, a Ph.D. student at the University of Waterloo in Ontario, Canada, and a member of the Covid Watch team. Leibrand says other teams independently developed “nearly identical” designs, though, and it’s unclear which may have influenced Apple and Google.

Uncertainty remains over whether enough people will use the apps to make the system truly effective—particularly in countries like the U.S., where their use is almost certain to be voluntary. Trust in the system’s anonymity could be key to widespread U.S. adoption.

Spokespeople for Apple and Google cited Oxford University research estimating that 60% of a population using a combination of contact tracing apps and widespread testing would be enough to contain the coronavirus pandemic. Lower adoption rates could still help control the virus’s spread.

The system developed by Apple and Google could be used for apps worldwide, including in countries that are more aggressive about collecting data about users. In addition to the decentralized Apple-Google system, some apps may include more centralized or detailed tracking, such as sharing GPS data.

Raskar, from MIT, says that additional data would generate more detailed public health insights, such as “heat maps” identifying geographic areas with high infection or transmission rates.

Variations are expected between the designs of apps relying on the Apple-Google system, likely including how cases are reported. One major hurdle to rolling out digital contact tracing is determining how to give doctors the ability to confirm cases through apps, if health authorities choose to implement that feature, according to White.

This and other issues to be worked out between developers and state health authorities will be a major factor in how soon apps are available, she says. Once Apple and Google release their new protocol in May, she estimates the apps using it could be available as little as one week later.

“We have the technology,” says White. “The issue now is working with states.”

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