Virginia’s coronavirus notification app, called Covidwise, launched on Wednesday, just under four months after the Apple–Google partnership was first announced.

Virginia is the first state in the United States to use the Apple-Google technology built into iPhones and Android phones. The exposure notification technology and contact-tracing apps were once heralded as a critical part of some countries’ strategies to lift their lockdowns, but low adoption and unclear effectiveness in some countries have dampened enthusiasm for the apps. 

Virginia’s app, like all apps using the Apple-Google framework, uses Bluetooth signals on a smartphone to determine how closely and for how long two phones were nearby, without collecting the location of the contact or the identity of the users. Then, if one of the phone’s users were to test positive for Covid-19, the system is able to notify any other phones with the app that they might have been exposed to the virus through a push notification and tell them to get tested or quarantine. 

“For the purpose of this app, there wasn’t an absolute need to be able to track where you are or who you are,” Jeff Stover, director of the Virginia Department of Health, said on a video call with reporters. “The most important thing was that you know whether or not you’ve potentially been exposed, and that we can all take actions to do whatever prevention is necessary.” 

When users test positive for Covid-19, they get a six-digit pin number provided by the Virginia Department of Health that they can input into their app. That six-digit pin unscrambles a database of encrypted contacts, which allows the system to send push notifications to people who may have been exposed. 

The app wasn’t built by Apple or Google — the two tech giants built software into iOS and Android to make it possible. Virginia paid SpringML $229,000 to develop the Covidwise app, and it was funded by the CARES act, Stover said.

Other states in the U.S. have released similar apps, but some of them, such as one in Utah, have used a location-based approach instead of Apple-Google system, which requires apps using it to eschew GPS and emphasizes anonymity. Apple and Google have also said they will turn the system off when the pandemic is over. 

One of the most successful exposure notification apps using the Apple-Google system is in Germany. The app, called Corona-Warn-App, was downloaded over 16 million times at the end of July out of a population of 82 million, according to the BBC. In France, which used a different Bluetooth system not backed by the tech giants, only 14 people were notified using the app over its first three weeks. 

One issue with the apps is that they will need to be installed by a large percentage of the population to work effectively — if a phone isn’t running the app, then it will miss potential exposures. One study by researchers at Oxford University suggested that 60% of the population would need to install an exposure notification app to suppress the virus.

“Effective is going to be anyone’s guess as how you want to describe that. But they also state in the [Oxford] study that they estimate that for every one to two app users, you will potentially reduce the infection by one,” Stover said. 

Virginia plans to heavily advertise the app on billboards, digital ads, and through partnerships with schools and workplaces, and Google has offered advertising credits for its search engine and Google Play app store, officials said. 

Google said last week in a blog post that 20 states and territories are “exploring” apps based on the system. While the app works outside of Virginia, positive tests require a six-digit pin from the Virginia Department of Health to notify others, effectively limiting its range. 

There is no plan for a national coronavirus exposure app, but Virginia officials said that the state is likely to participate in a program building a “national key server” that would enable apps from different states to work together.