Big tech's contact tracing apps won't be a silver bullet to stop COVID-19 — we need more human tracers making actual phone calls

• Health experts say contact tracing must be a fundamental part of countries' attempts to reopen amid COVID-19.
• Contact tracing is a tried-and-true technique to find and isolate people who are carrying an illness to slow the virus' spread.
• Some governments are turning to tech giants like Apple and Google that are building tech using smartphones' Bluetooth capabilities to track when people come in close contact with someone carrying the virus.
• But contact tracing apps won't work unless the majority of people opt in — and two studies published this week indicate most people can't or won't use smartphone-based contact tracing tools.
• There's a much simpler contact tracing technique that has been proven to work: Hiring an army of human contact tracers to make phone calls to people potentially exposed to COVID-19.
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As countries aim to reopen amid COVID-19, health experts across the globe are in near-unanimous agreement: contact tracing will be crucial in order to stop further outbreaks.

Contact tracing is a decades-old public health technique that's been used to fight past outbreaks including HIV, Ebola, and measles. It's part of a multi-pronged approach, along with testing and isolation, to identify people who were potentially exposed to a virus in order to slow the spread.

Tech companies are now pitching smartphone apps in the global push to expand contact tracing. State and national governments worldwide have begun contracting with tech companies to build apps that would use Bluetooth or GPS location data to monitor when people come in contact with someone who's been identified as a COVID-19 carrier. Apple and Google are set to release an ambitious contact tracing technology for iPhone and Android users in the coming weeks.

These high-tech solutions have been touted as a silver bullet in the fight against coronavirus. But contact tracing apps are already running up against an early barrier to effectiveness: Most operate on an opt-in basis, and not everybody wants to use them.

Contact tracing apps won't work unless almost everyone is using them. Early signs show that's unlikely to happen.

Singapore was one of the first countries to roll out a Bluetooth-powered contact tracing app in early March. At first, it appeared to be part of an effective COVID-19 response. The country reported fewer than a 300 cases in mid-March — but by mid-April, COVID-19 in Singapore was surging out of control. Now, Singapore has more than 15,000 confirmed cases.

Part of the problem: Only 10% to 20% of Singapore's population ever downloaded the contact tracing app. Without a critical mass of users, the majority of people were going untraced.

Two studies published this week signal that Apple and Google could face the same problem in the US, where one in six people don't even have a smartphone.

A Washington Post-University of Maryland poll found that nearly three in five Americans say they would be unwilling or unable to use Google and Apple's contact tracing technology. A different survey by researchers at Microsoft and the University fo Zurich found that 60% of Americans said they're willing to use COVID-19 tracing technology, but fewer than 20% of respondents said they'd use it if it came from a tech company.

Contact tracing tech has been a part of successful COVID-19 response in some places, including China and South Korea. But in both countries, the government mandates that people use tracking apps, whereas Apple and Google's technology would be strictly opt-in.

There's a more straightforward contact tracing method that's proven to work: Hiring an army of human tracers.

Success stories in China and South Korea, where COVID-19 outbreaks have been largely brought under control, were aided by huge numbers of human contact tracers who call people infected with COVID-19, ask who they came into contact with, and subsequently alert those people to slow the spread.

The US federal government employs only 2,200 contact tracers. Some states are already taking steps to bolster that number: Massachusetts has hired 1,000 new tracers; California plans to hire 10,000 across the state; over 1,000 are being hired in New York City. For comparison, China hired 9,000 contact tracers in Wuhan, a city of 11 million people.

The Johns Hopkins Center for Health Security estimates that the US needs to hire roughly 100,000 new human contact tracers for contact tracing to be effective.

One of the lead developers of Singapore's contact tracing app, Jason Bay, has provided some perspective on how such technology stacks up to human tracers. Bay wrote in a blog post earlier this month that he believes people shouldn't put too much faith in high-tech solutions.

"If you ask me whether any Bluetooth contact tracing system deployed or under development, anywhere in the world, is ready to replace manual contact tracing," Bay wrote, "I will say without qualification that the answer is, No."