SILICON VALLEY’S new motto during the coronavirus pandemic is to move fast and fix things. Technologists have created contact tracing systems to help get us out of this crisis and out of our houses, but the narrow debates surrounding the inventions miss a reality: Any digital solution to our problem that’s sufficiently privacy-protective also won’t be sufficiently useful without a lot of humans in the loop.

Apple and Google have built a Bluetooth-based tool that, in combination with apps built by states and localities, will notify users who have come into contact with someone who has self-reported a covid-19 diagnosis. Many governments around the world are sparing themselves technical headaches by accepting the companies’ vision as their own. Others are not, primarily because they want to control more data than the companies will permit.

Those hanging on to dreams of this so-called centralized model include France and Britain. Regulators in Britain argue that holding the anonymized data of those the infected have encountered will allow them to decide which citizens to notify and which to leave alone, as well as to analyze the types of interactions most likely to result in transmission. Those pushing the decentralized model argue that proximity data isn’t as anonymous as it seems and so could allow for too much government monitoring. They argue further that the crucial ingredient to success is trust: The less like a dragnet a tracing tool looks, the more people will use it — and use it in a way that’s helpful to stemming outbreaks.

The dispute obscures the fact that neither method, as long as it puts anonymity at the center and as long as it leaves location aside as most Western liberal democracies have pledged, can come close to a substitution for manual efforts. That doesn’t mean the systems aren’t valuable, but their value shouldn’t be overstated.

Contact tracing as traditionally conducted relies precisely on a lack of anonymity. It requires knowing names, addresses and routines to follow extended chains of transmission and also cajole people, through person-to-person interaction, into behaving responsibly. Apple and Google were wise to rename their system “exposure notification,” because that’s what it really does: reach those strangers with whom the infected have crossed paths that analog methods might not catch.

What happens then will depend on old-fashioned public health policy. Authorities could ask people who receive exposure pings to stay indoors, but they could also ask them to take self-assessments providing information about, say, any gatherings in large groups or other risky activity — and then, perhaps, to call a manual contact tracer. In the meantime, manual tracers will be freed up to focus on close contacts of the infected. And when they happen to reach someone who’s already isolating because they’ve received a phone ping, their work becomes that much easier.

These responses taken together can give governments the insight they need to understand where and how outbreaks are happening, and hopefully to stop them. But there’s no app that can do the job on its own.

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