This week, California residents received push notifications on their smartphones asking them to log into CA Notify, a system that allows users to anonymously alert users that they may have been exposed to the Covid-19 coronavirus.
CA Notify, which officially launched on Thursday, is based on technology Apple and Google developed earlier this year. These exposure notifications use Bluetooth to measure when people have been close to each other for an extended period of time, indicating a possible transmission of coronaviruses without collecting personal information.
The app is designed to alert users that they may have been exposed to potential coronavirus infection at an early stage so they can be tested or quarantined before they spread the virus.
California is the most populous of 19 US states that have so far introduced an exposure notification system, and the state where both Google and Apple are headquartered. The app is released as 80% of the California population were ordered to stay home for three weeks.
Due to the way the system was developed, the California Department of Health (CDPH), which operates CA Notify, does not provide accurate statistics on the number of activations. However, the department estimates that 4 million Californians activated the system on their phone as of Friday based on the number of times a particular URL was accessed on their server.
California has just under 40 million residents, making it roughly 10% of the state’s population so far.
CA Notify is the largest test to date for Exposure Notifications Express, an update to the Google Apple framework announced in September that is intended to promote acceptance. It enables governments to send push notifications to users that the apps and system are available in their region.
CA Notify works with both iPhones and Android phones, but requires a device that can run the latest software. On iPhones manufactured after 2015 with the latest software, CA Notify can be activated in the Exposure Notifications section in the Settings app. People with eligible Android phones can download an app from the Google Play Store. The app is available in 15 different languages.
California said the app compliments other public health interventions like wearing a mask, social distancing, and hand washing. Exposure notifications are also different from contact tracing, a practice in which health officials manually contact people who have tested positive in order to find other people who may be at risk.
Instead, exposure notifications exchange random sequences of letters and numbers between phones via Bluetooth. If someone tests positive with the app, they will receive a text message with a code from the California health department. They enter this code into their app or system and send an alert to other people who have been within six feet for more than 15 minutes to let them know of possible exposure to someone with Covid-19 without the Revealing the identity of the person who tested positive.
The alert does not provide any information about the location, time, or identity of the close contact, but does notify the user of the date it was recorded.
Earlier this year, a major problem with exposure notification apps in the US was that they did not work across state lines. In the US, these apps are developed at the state level rather than a national app like in the UK. However, as of December, 18 states, including California, are participating in a national key server program that allows the system to work across functional status lines even though they are different apps.
Adoption remains a problem for these apps, especially in the US. They generally work better with more people attending, as more devices track potential close contacts. A study earlier this year found that 60% of the population would need to use one of these systems to stop the transmission of Covid-19. However, later research suggests that lower intake may slow the spread of the virus even further.
The early adoption rate in California has been more robust than some major earlier states, and this is largely due to push notifications that went out to Californians on Thursday.
To increase acceptance, Apple and Google introduced an update for their system in September, which is known as Exposure Notifications Express. California uses Exposure Notifications Express. Instead of building a full app, governments can instead send a configuration file to Apple and Google and get the system up and running quickly. iPhone users don’t even need to download an app from Exposure Notifications Express.
But perhaps most importantly, health officials can send push notifications to residents when the system is available, which encourages adoption.
So far, not all Californians have received push notifications, but they will continue to run out until they are sent to all smartphones in the area, CDPH said in an email. Apple sends notifications to iOS users and Google to Android users who are physically located in California. If people get the alert, it depends on the phone’s location, CDPH said. Someone staying at home for several days might not get a notification until the next time they go to a new location.
Exposure Notifications Express has increased adoption in the regions where it is used. Google said Friday that in Colorado, 20% of the people have chosen that state’s system. In Washington DC, 367,000 people have joined the system, representing 53% of the district’s population.
Both health authorities use Exposure Notifications Express. EN Express systems were also deployed in Connecticut, Maryland and Nevada, which used the system to send a push notification to residents despite the presence of the app.
Measuring the effectiveness of these systems is also difficult as they are designed in such a way that health authorities cannot collect personal information such as the name, phone number or identity of contacts in order to measure how many potential infections the trapped apps would not be on any other Way has been discovered.
In a trial period that tested CA Notify at several California universities, approximately 28,000 people took part in the system and issued 80 codes that a user could use to alert those who might be nearby, CDPH said .
Google says there are “other anecdotal signs” that the exposure system is helping, citing an episode where the Virginia governor tested positive and his staff received notifications.