Skip to main content

How Apple and Google are tackling one of the toughest parts about tracking COVID-19 exposures

How Apple and Google are tackling one of the toughest parts about tracking COVID-19 exposures


Adoption is the hard part of contact tracing apps so far — but if it’s baked into the operating system, it gets a lot easier

Share this story

Apple Google iPhone Android (1020)

Around here we say that The Interface comes out Monday through Thursday, and on particularly newsy Fridays. Well, today was a particularly newsy Friday. Here’s your emergency newsletter ...

On Thursday evening I wrote about some of the limitations in using the Bluetooth chip in your smartphone to track the spread of COVID-19. Naturally, on Friday morning Apple and Google announced what might be the most significant collaboration in the history of both companies — a joint effort to use the Bluetooth chip in your smartphone to track the spread of COVID-19.

Russell Brandom and Adi Robertson had the details in The Verge:

The new system, which is laid out in a series of documents and white papers, would use short-range Bluetooth communications to establish a voluntary contact-tracing network, keeping extensive data on phones that have been in close proximity with each other. Official apps from public health authorities will get access to this data, and users who download them can report if they’ve been diagnosed with COVID-19. The system will also alert people who download them to whether they were in close contact with an infected person.

Apple and Google will introduce a pair of iOS and Android APIs in mid-May and make sure these health authorities’ apps can implement them. During this phase, users will still have to download an app to participate in contact-tracing, which could limit adoption. But in the months after the API is complete, the companies will work on building tracing functionality into the underlying operating system, as an option immediately available to everyone with an iOS or Android phone.

If you’re new to the idea of how contact tracing helps to stop the spread of diseases, start with this explainer from my colleague Nicole Wetsman. Public health agencies have long dispatched workers, both on foot and over the telephone, to get in touch with people who may have been exposed to someone who is carrying an infectious disease. In light of the COVID-19 pandemic, countries around the world have been experimenting with apps that attempt to use the widespread adoption of smartphones and the signals they receive to identify new potential cases. And as I laid out yesterday, public health officials I’ve spoken with have expressed skepticism about the effectiveness of such efforts.

First let me say that I’m glad to see big corporations working hard on the COVID-19 response, and working together. Quick, bold action can save lives, and it’s fine that not everything that gets tried will work perfectly — or at all. It’s also true that given how many questions remain around the Apple/Google collaboration, it’s impossible at this point to say how effective it might be. I hope it’s very effective!

That said, Bluetooth-based approaches to contact tracing have at least three big problems, experts have told me. (Privacy, surprisingly, really isn’t one of them, at least not to me; the privacy design of the Apple/Google system is quite clever. Moxie Marlinspike has some quibbles, though.) The bigger problems are: it’s hard to get people to download a new app, Bluetooth signals can be unreliable, and a focus on tech solutions could reduce pressure on public health agencies to hire people to do contact tracing, even though there’s much more evidence of those workers’ effectiveness than there is for smartphone apps.

So, let’s look at how the Apple/Google collaboration seeks to address some of these points.

The most significant part of the problem that the API project attempts to handle is adoption, particularly in the second phase of the project. Apple explained it to me like this: once you update your phone to the latest version of the operating system, and opt in to the contact tracing API, your phone will begin sending out Bluetooth signals to nearby phones and recording signals sent to it by other phones. The best part of this system is that it works retroactively — once you download a public health app tied into this system, it will share your “proximity events” from the past 14 days. Adi Robertson details the process here.

By creating a central API across our two major smartphone operating systems, Apple and Google are providing a valuable tool for public health agencies working on contact tracing apps that will work across jurisdictions around the world, even as people begin to resume travel. It’s hard to imagine something like this being done in any way but at the level of the operating system; only these two companies could make something like this possible.

An open question is whether you’ll get pinged about exposure if you’ve updated your phone OS but haven’t downloaded a public health app. It seems like the answer is yes, based on what we’ve seen — which would go further toward addressing the issue of adoption than any other proposal I’ve seen. If the answer is that you still have to download an app to receive the notification, the basic problem hasn’t really gone away.

We’ll see.

So what about the reliability of Bluetooth signals? A strong signal has a range of about 30 feet — much further than the 6-foot distance that authorities have asked the public to maintain. And the signal is binary, not relative — it can say only “these two phones came in close proximity” rather than “this phone was 6 feet from that phone.” That raises the concern that many of the proximity events recorded by our phones will be false positives — cases where you were relatively close to someone who reported an infection, but may have not been close enough to become infected yourself.

Apple says it’s still investigating all this, but notes that public health apps will be able to include duration of proximity when deciding what counts as a proximity event. (The suggested time I heard today was five minutes.) At a five-minute interval, you would be less likely to trigger false positives from someone who jogged by you on the street.

Which raises the question, what are circumstances during the pandemic where people are (1) within 30 feet of you, for (2) five minutes or more, that (3) you don’t really know? (If you knew them well, you would probably also find out that they had COVID-19.) Some suggestions I’ve heard today: grocery store workers; people waiting in long lines for things (like entry to grocery stores); warehouse workers; and mass transit. As cities begin to re-open, more use cases might emerge. But it does seem like a passive system that works to inform people in those situations about potential exposures could offer at least some level of protection. The question is whether the system ultimately generates more signal than noise — whether Bluetooth finds more true positives than false ones.

We’ll see.

Finally, is Silicon Valley leaning too hard on untested software solutions when a proven manual solution could suffice? That’s the argument in a paper this week from Duke University’s Margolis Center for Health Policy. Authors Mark McClellan, Scott Gottlieb, Farzad Mostashari, Caitlin Rivers, and Lauren Silvis write:

Ideally, when a new case of COVID-19 is identified, local public health officials will assure that the affected individual is isolated, and that their close contacts are identified and asked to quarantine. However, existing local public health capacity for such response activities is very limited, and many jurisdictions have abandoned contact tracing in favor of community-level mitigation measures. To enable a return to case-based interventions as incidence declines, these capacities need to be expanded. Improved capacity will be most effective if coordinated with health care providers, health systems, and health plans and supported by timely electronic data sharing. Cell phone-based apps recording proximity events between individuals are unlikely to have adequate discriminating ability or adoption to achieve public health utility, while introducing serious privacy, security, and logistical concerns. Instead, timely contact tracing can be achieved through strengthened public health case investigation augmented by technology and community-level collaborations. 

But other researchers have argued that COVID-19 simply spreads too easily to make manual contact tracing a feasible solution to the problem. Something passive and automated is necessary to counter the speed of transmission, according to a March paper in Science. Luca Ferretti, Chris Wymant, Michelle Kendall, Lele Zhao, Anel Nurtay, Lucie Abeler-Dörner, Michael Parker, David Bonsall, and Christophe Fraser write:

Traditional manual contact tracing procedures are not fast enough for SARS-CoV-2. A delay from confirming a case to finding their contacts is not, however, inevitable. Specifically, this delay can be avoided by using a mobile phone app.

Perhaps the best way to think about the Apple/Google announcement is that in a world with no coherent federal response to the ongoing disaster, we must instead rely on a patchwork of partial solutions. In such a world, I have no objection to Apple and Google trying to build a contact tracing tool, even if I do worry that people will expect too much of it. I am also, as ever, open to being pleasantly surprised.

We’ll see.

Those good tweets

Talk to us

Send us tips, comments, questions, and Bluetooth signals: and