Bill Gates thinks most countries will fight COVID-19 with interview-based contact tracing and a central database to track exposure. Gates posted a paper today outlining potential pandemic treatments, vaccines, and containment strategies. He calls contact tracing, which helps identify and isolate people who could spread the virus, an “ideal way” to stop the pandemic. But he downplayed the importance of decentralized tech-only options like those proposed by Apple and Google, focusing on more traditional methods combined with large-scale data analysis.

Gates believes privacy concerns will stop many countries from adopting GPS tracking like that used in South Korea and China. He also seems lukewarm on Bluetooth-based contact tracing systems, especially ones that operate without experts getting access to the data. “If most people voluntarily installed this kind of application, it would probably help some,” Gates writes. But he points out that someone can leave the virus on a surface where it’s later picked up by another person, even if the two never come near each other. These systems also require large-scale adoption that can be difficult to get.

“I think most countries will use the approach that Germany is using, which requires interviewing everyone who tests positive and using a database to make sure there is follow-up with all the contacts. The pattern of infections is studied to see where the risk is highest and policy might need to change,” writes Gates.

“Every health system will have to figure out how to staff up.”

This raises obvious privacy questions and would require huge numbers of interviewers, something Gates acknowledges. “Every health system will have to figure out how to staff up so that this work is done in a timely fashion,” he writes. “Everyone who does the work would have to be properly trained and required to keep all the information private. Researchers would be asked to study the database to find patterns of infection, again with privacy safeguards in place.”

While Gates doesn’t mention it, Germany is one of the prime drivers of a Bluetooth-based contact tracing initiative called the Pan-European Privacy-Preserving Proximity Tracing project. The system is similar in some ways to Apple and Google’s plans for a tracking system built into iOS and Android. But the anonymized data would be held on a central server, while Apple and Google have favored a system that’s supposed to store as much data as possible on users’ devices. (There’s still a lot we don’t know about its process.) Meanwhile, a separate group of experts has proposed a system called Decentralized Privacy-Preserving Proximity Tracing.

American health authorities are attempting to rapidly scale up a contact tracing interview system that may require an “army” of disease detectives. Massachusetts recently budgeted for 1,000 people to interview infected citizens over the phone and determine who they’ve been in contact with. The Centers for Disease Control and Prevention also sent contact tracing teams to eight states. Tracing efforts also depend heavily on having a robust testing system, which the country has been slow to roll out.

Gates’ views on the pandemic are fairly mainstream, but he’s become a target of conspiracy theorists in recent weeks. Former Trump adviser Roger Stone made headlines for repeating a baseless claim that Gates wants to microchip people who receive a novel coronavirus vaccine, misinterpreting a comment the Microsoft co-founder made in a Reddit AMA. This week, right-wing extremists circulated a list of email addresses and passwords that included members of the Gates Foundation, prompting claims of a hack — but the credentials appeared to be cobbled together from past data breaches.