More than six months into the COVID-19 pandemic, a handful of U.S. states are starting to roll out apps that promise to tell people if they've been exposed to someone with the virus - without revealing personal information.

Now with the White House struggling with a COVID-19 outbreak, the goal to figure out a way to quickly notify people has gained more urgency.

The arrival of these apps in the U.S. comes as communities are opening in fits and starts. The hope is that by using technology to notify people they've been exposed to the virus, the apps will enhance the ability of local health officials to stem the spread of COVID-19.

It's an idea being tested - in real time.  But will the apps make a difference?

"We don't know yet," said Jeffrey Kahn, director of the Johns Hopkins Berman Institute of Bioethics. "That's part of what's both interesting and frustrating about where we are. This is an unproven technology. It's being rolled out in the midst of a public health emergency. There's a lot of learning as we go as a result."

Notifying people, anonymously

While state apps vary, the primary approach being used in the U.S. is based on technology from Apple and Google:

A person downloads an app created by their state health department. Using the person's mobile phone technology, the app begins collecting anonymized information about other phones it comes near - which phones, how close and for how long. That information of the "digital handshake" is stored on the person's phone.

If a person tests positive for COVID-19, health officials give that person a code to put into the app. An alert then goes out to others who have the app who have been near that person in the prior two weeks.

Two approaches

Covid apps for mobile phones first appeared in Asia, in China and South Korea. There, officials used a phone's location information to track people.

It's an approach being used in other parts of the world. In Israel, the government is scouring people's mobile phone records to locate those who've been near someone who has tested positive in order to possibly quarantine those people. In Turkey, a person's mobile phone software tracks their movements and who they've been near.

But approaches that use a phone's location information raise privacy questions, said Megan DeBlois, a systems security graduate student who helped to create the COVID-19 App Tracker, a website that keeps track of Covid apps around the world.

"There are too many apps that request far too much," she said.

Anonymous users

U.S. states are creating their own apps, based on the approach offered by Apple and Google, which made it a condition of using their technology that the COVID-19 apps couldn't use mobile phone location data.

That privacy requirement helps build people's trust in the apps, said Sarah Kreps, a government professor at Cornell University who is studying COVID-19, technology and public sentiment. Knowing someone who has been infected by the coronavirus that causes COVID-19 also makes people more willing to try a COVID-19 app, she said.

"In order for these apps to be effective, you need to have enough of a critical mass of people who are willing to download and use the app," she said. "And short of mandating that, as was done in China, then you need a kind of public trust."

So far in Virginia and other states with COVID-19 apps, people recently interviewed appeared open to using the apps.

"I'm trying to be personally conscious, responsible, for what I should be doing," said Mike, who was recently on a bike path in Northern Virginia. "This was billed as something you can trust, and I accept it."

"I read up on it and honestly I feel pretty good about it," said Hayes, a graduate student at University of Arizona who planned to download the CovidWatch app. "They've done a lot of stuff to avoid privacy issues. I think it sounds pretty legit."

Limits of privacy

But anonymous COVID-19 apps come with a trade-off: They limit the app's usefulness to public health officials. If a person's identity and location aren't known, the app gives scarce information about an ongoing outbreak.

Joyce Schroeder heads the molecular and cellular biology department at the University of Arizona and has been the lead in developing CovidWatch, an Arizona-based app that doesn't collect individuals' private information.

That's "a good thing," she said. "We want to have our privacy. But it's also a frustrating thing when you're trying to collect data on something and find out if it's working. There's very little data that we can collect on the app."

States working together

Outside the U.S., countries' health departments have been issuing nationwide apps. In the U.S., the federal government isn't doing its own app so states have contracted with app developers to create their own.

So far, nine states have issued COVID-19 notification apps based on the Apple-Google technology with more states working on their own, according to a review by 9to5Mac.

In its latest software update, Apple installed something called Exposure Notification on mobile devices so that states can more easily start notifying people if they've been exposed. Users can turn it on or off. Google is expected to issue the same Android update soon.

Working with Microsoft, the Association of Public Health Laboratories recently launched a "national key server," which will make it possible to use an app from one state while visiting other states.

While it's too early to say, these efforts to use technology may make a difference in the fight against Covid, said Johns Hopkins' Kahn.

"It's an opportunity," he said, "to help steer the positive use of a technology during what are obviously very challenging times."

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