Coronavirus Apps Don't Need 60% Adoption To Be Effective

With dozens of digital contact tracing apps already rolled out worldwide, and many more on the way, how many people need to use them for the system to work? One number has come up over and over again: 60%. From a report: That's the percentage of the population that many public health authorities documented by MIT Technology Review's Covid Tracing Tracker say they are targeting as they attempt to protect their communities from covid-19. The number is taken from an Oxford University study released in April. But since no nation has reached such levels, many have criticized "exposure notification" technologies as essentially worthless. But the researchers who produced the original study say their work has been profoundly misunderstood, and that in fact much lower levels of app adoption could still be vitally important for tackling covid-19.

"There's been a lot of misreporting around efficacy and uptake ... suggesting that the app only works at 60% -- which is not the case," says Andrea Stewart, a spokeswoman for the Oxford team. In fact, she says, "it starts to have a protective effect" at "much lower levels." The Oxford models found that "the app has an effect at all levels of uptake" as illustrated by this graph which shows every level of adoption slowing to pandemic to some extent. Because of the way such digital contacting tracing and exposure notification apps work -- by notifying users if their phone has been in proximity to the phone of somebody who later gets a diagnosis of covid-19 -- blanket coverage is preferable. The greater the number of users, the higher the likelihood that it will help at-risk people to self-quarantine before they can infect others.

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