Screenshots of two COVID-19 apps for exposure notification.
Contact tracing apps that warn people who may have been exposed to the coronavirus are being developed in Alabama (left) and North Dakota.
Photo: Courtesy of the University of Alabama at Birmingham and ProudCrowd
  • Apple and Google this spring developed a system that enables states to build apps to alert people if they've been exposed to someone who tests positive for COVID-19.
  • The first apps were expected by early June, but none have been released, and few are in development.
  • Health officials are grappling with open questions as they develop apps, including how to define a risky encounter with someone carrying the virus.

In May, Apple and Google released the tools needed to build mobile apps that notify smartphone users about potentially risky encounters with people who later test positive for COVID-19. The apps would help with contact tracing, which is considered a vital tool for stopping the pandemic.

A few states said they’d release the first apps in a matter of weeks. More states, it appeared, would soon follow. But two months later, no exposure-notification app has yet been launched in the United States.

Meanwhile, some states began allowing businesses to reopen en masse, contributing to deadly spikes of new coronavirus infections from Idaho to Texas to Florida. U.S. cases surged well past 3 million last week, with 62,918 new cases reported on July 12 alone.

The Apple-Google system was supposed to help prevent infections at this scale, in cooperation with wide-scale testing for the virus. Your smartphone would anonymously log encounters whenever you were near another person for a set length of time, assuming they also had the app on their phone.

Then, if one of those people later tested positive for COVID-19, they could notify the app, and the app would alert you. Everyone's identities would remain hidden from each other, and no data would be shared with the tech companies. But you'd find out that you might have been exposed to the virus, and you could self-quarantine right away to avoid spreading the disease.

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This process would alleviate some of the fast-increasing burden on low-tech, human contact-tracing teams, which already face dire staffing shortages around the country. Contact tracing, through phone calls and old-fashioned gumshoe reporting, has been a proven tool for slowing the spread of infectious disease since at least the 1930s.

It has been used successfully to control outbreaks of Ebola and SARS, and of COVID-19 in several other countries.

But in interviews with CR, public health officials and software developers say technical difficulties and coordination challenges have held them back from releasing contact-tracing apps.

North Dakota predicted it would have an app ready by early June. “But then we realized when we got into it that there’s some assembly required,” says Tim Brookins, the developer behind Care19, the state’s official tracing app. “It’s like you get your Christmas present and it’s in a million pieces,” he says. “And some of the pieces are missing.”

Front-runners North Dakota and Alabama say they are still weeks away from releasing their contact tracing apps. South Carolina, Arizona, Virginia, and Washington state are at various stages of building apps, too, but they’re even further from launch. Most of the remaining states don’t have any apps in the works at all, according to reporting by Business Insider—at least none based on the Apple-Google technology.

Experts tell CR that several states are waiting on the sidelines to see how the early movers fare. Here are the thorny questions that need to be answered—both for health officials and the public—before the apps can roll out and potentially help control the pandemic.

How Close Is Too Close?

The apps are supposed to tell you if you’ve had a risky encounter with an infected person. But how do you define a risky run-in? That's the biggest decision health departments have to make.

The Centers for Disease Control and Prevention estimates that two people are in "close contact" if they remain within 6 feet of one another for more than 15 minutes. But states have free rein to set the time and distance parameters in their apps.

States where the disease is rare could be “a little more aggressive,” says Janet Hamilton, executive director of the Council of State and Territorial Epidemiologists (CTSE). They might decide to narrow that 15-minute window, for example, to trigger more alerts and try to stop the infection from gaining a local foothold.

But you wouldn’t want to do that in a state with lots of cases, because people might get swamped with too many alerts, eroding trust in the system and prompting people to delete the app. Instead, health officials might pare back on notifications to only pinpoint the very riskiest encounters, while stepping up measures such as ordering people to shelter at home. “I don’t think there is necessarily a one-size-fits-all solution,” Hamilton says.

North Dakota and Alabama are sticking to the 6-foot, 15-minute defaults for starters, according to health officials and developers in the states. But, in the future, a state may be able to allow for different settings in different environments.

When users sign up for an app, they may be able to indicate that they’re affiliated with a participating university or workplace. And that’s when the default definition of an exposure might change drastically: On a campus, administrators could customize the parameters to fit their needs. For example, an alert could be triggered if someone was within 20 feet, for an hour or so, of a person who later tests positive. That’s according to Brookins, the North Dakota app developer, who has heard from several universities that are interested in implementing contact tracing.

Your university or employer could also send you a tailored message if you’ve had a run-in with somebody who tested positive for the coronavirus. They could ask you to visit the college clinic and self-isolate in your dorm room, for example, or to notify HR so your team at work can get tested.

Brookins says Apple and Google have been enthusiastic about the ability to customize these rules, but have not yet formally approved the feature. Apple, for its part, tells CR these decisions are up to health departments.

The University of Alabama is developing the state’s contact-tracing app, and some of the first users could be on its campuses. The administration has said that it will strongly encourage—but not require—students, faculty, and staff to download and use the app. Apple and Google aren't allowing use of their apps to be mandatory, no matter where they're used.

Initially, at least, the University of Alabama app won't treat campus-goers differently from anyone else.

“I think this is a good idea, if we're able to implement it correctly,” says Kathryn Tune, a University of Alabama graduate student.

“It all depends on when the app goes live, how user friendly it is, whether it works correctly, and more,” she says. “If it works as it's proposed, yes, it will make me feel more comfortable. [But] if I see that students aren't using it, it's buggy or difficult to use, or not marketed well, it will seem pretty futile in my mind.”

Some other colleges and universities, from liberal arts colleges like Middlebury College in rural Vermont to Boston's Northeastern University, won't have access to an app built on the Apple-Google technology because their state's aren't planning to create apps any time soon.

Instead, the schools are building or licensing simpler tools that ask community members to use an app that screens them for symptoms before coming to campus each day. They say they may add exposure-notification later on.

Northeastern is among the institutions that says it will require campus-goers to use the app, and to get regularly scheduled tests for the virus.

Will Apps Work Across State Lines?

It’s important for everyone who meets other people to use the same contact tracing system. If shoppers at the same supermarket were all using different apps, many close encounters might not be detected and reported.

Apple and Google are addressing that problem by allowing only one health agency per state to build one of the new apps. But in many parts of the country, that’s not sufficient. 

“Here, you could travel two hours and you’ve crossed a state line, and that’s not very far,” says Sue Feldman, director of graduate programs in health informatics at the University of Alabama at Birmingham, which is helping develop the app.

Imagine that you live in one state and work in another: If you test positive and report the result to your home state’s contact-tracing app, only other users in that state will be notified that they were exposed to you. Anyone you came near at work would never know that you tested positive, because they would be using a different app.

The best solution, public health experts say, is to create one nationwide server that will power exposure-notification apps no matter where they're used in the country. Brookins calls this the last big remaining obstacle to releasing these apps.

The Association for Public Health Laboratories has taken charge of setting up this nationwide server. APHL already compiles all kinds of medical lab data from around the country, and maintains the foundations for Sara Alerts, a case-management system that human contact tracers are using in Virginia, Arkansas, Arizona, and elsewhere. 

Will Users Have to Share Personal Details?

Apple and Google have put stringent privacy requirements in place for apps that use their technology. For instance, they don’t allow apps to ask for a user’s GPS location.

But apps are allowed to ask for some basic personal information. As noted above, an app could ask if you want to identify yourself as a member of a particular university or workplace. An app could also request a phone number to allow human contact tracers to get in touch later. Apps are also allowed to ask for users’ ZIP codes, to alert public health officials to detect localized outbreaks. These questions would be optional.

Hamilton, from the CTSE, says Apple and Google have considered letting the apps ask for permission to collect other types of information, too. These include details like exactly when an exposure occurred, which could allow the app to give you more targeted advice on what to do next. 

Adding more details could also help the app tweak other kinds of messages. If an app were allowed to ask for your age range, or about medical conditions that make people more susceptible to COVID-19 complications, it could give you a special set of instructions along with an exposure notification.

Will the Apps Be Accurate?

It’s one thing to make critical decisions about how these public health apps should work, but actually building them presents a whole other set of hurdles.

Say a public health agency decides to go with the CDC’s 6-foot, 15-minute guideline for defining a risky exposure. The time part is easy, but the distance isn’t. “It turns out the phone can’t actually measure distance; what it can measure is signal strength,” Brookins says. 

The apps calculate distance based on the strength of Bluetooth signals. However, lots of things can affect those signals. Two people sitting on a park bench would look very different to their exposure-notification apps depending on which pocket their smartphones are in, Brookins says. In one case, their phones could be less than a foot apart, with antennas facing each other; in another, the phones could be in their outside pockets, the signals partially blocked by their bodies. 

And an app might record an encounter even if you and another user were seated safely on either side of a window.

"Bluetooth is still not that refined," says Feldman of the University of Alabama at Birmingham. On campus, testers have been walking around with phones in their pockets to see how the app registers encounters in various settings. 

The results could vary depending on what kind of phone you have, too.

In Latvia, one of the first countries to develop an app with the Apple-Google system, testers found discrepancies in distance readings when they experimented with several hundred different phones, according to Arvis Zeile, CEO of MAK IT, a Latvian tech company helping develop its country’s app.

This doesn't mean the apps won't work—they simply may not be down-to-the-foot precise when it comes to deciding whether an encounter with someone with COVID-19 was risky or not. But a high level of precision is less important than getting these apps into people's hands, public health experts say.

“Every day that we have delays—whether it’s getting lab data into public health with complete race and ethnicity information, getting an electronic health report, or implementing new tools for exposure notification—any delay leads to potentially lost lives and additional cases,” says CTSE's Hamilton.