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Po-Shen Loh and Ariel Procaccia

Contact Tracing Didn't Defeat Covid. Here's How It Could.

Appealing to self-interest instead of relying on social obligation would provide incentives to cooperate that were missing early in the pandemic. There’s an app for that.

Nice try, Hong Kong.

Nice try, Hong Kong.

Photographer: Bertha Wang/AFP via Getty Images

Remember contact tracing? Early in the Covid-19 pandemic, it was seen as the first line of defense against the virus. The idea was that public health workers could be mobilized to contact everyone who’d been infected or exposed, and then would warn friends, family, neighbors and colleagues to lie low.

Nice try. It turned out that a veritable army of contact tracers would have been needed to effectively respond when cases surged. And something else was missing, at least in parts of the U.S., where people contacted by tracers helped identify less than one contact on average per Covid case (versus 17 in Taiwan). Maybe Americans were shockingly reclusive or, more plausibly, just didn’t trust government.