Updated Sept. 4, 2020

As we start to see exposure notification apps rolling out around the world, we’ve been frequently getting questions about what level of adoption communities need to have the apps be effective. 

Many ask us about the oft-mentioned 60% threshold that comes from a highly-cited article out of the Coronavirus Fraser Group at Oxford. The researchers simulated coronavirus in a model city and found that “we can stop the epidemic if approximately 60% of the population use the app, and even with lower numbers of app users, we still estimate a reduction in the number of coronavirus cases and deaths,” explained Professor Christophe Fraser, senior author of the latest report from Oxford University’s Nuffield Department of Medicine.

Recently published research results by the Coronavirus Fraser Group using real data from Washington State provide more nuanced modeling around the impact of exposure notification: “In a model in which 15% of the population participated, we found that digital exposure notification systems could reduce infections and deaths by approximately 8% and 6%, effectively complementing traditional contact tracing.”

Clearing Up Confusion

But somehow, the research has been misunderstood and mis-reported with the 60% figure having “a mind of its own,” and leading people to think that exposure notification will only work if use is that high, explains a fantastic article from MIT Technology Review. As the original research shows, coronavirus apps don’t need 60% adoption to be effective and exposure notification may work at much lower levels of usage than most people think.

The MIT article notes, “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.”

Chart showing the reduction in cases at 0%, 14%, 28%, 42% and 56% uptake in app usage. As uptake increases, total new cases decreases in a non-linear fashion.
Source: MIT Technology Review

Exposure Notifications: One Element of Intervention

Even just 14% of the population using the app can be helpful in slowing the spread of the virus, and once you start to get into the mid-20s the effect can become quite substantial. To get the same results as the model it is important to have test results returned quickly – the longer the delay for test results and notification in the app, the smaller the effect of the intervention.

Of course, this highlights the fact that nobody expects an exposure notification app to be the only element within their test, trace, and isolate strategy. Every public health agency (PHA) is looking at exposure notifications as one element within a broader public health intervention. 

The Coronavirus Frase Group’s new research from September explores this effect in even more depth: “We find that for all three counties, manual contact tracing at the recommended staffing levels combined with an exposure notification app can significantly reduce the amount of time it takes to achieve this metric. Under the recommended standard for manual tracing, adding exposure notification at 30% adoption results in reaching the target in 92%, 87%, and 85% of the time versus no exposure notification for King, Pierce, and Snohomish counties respectively.”

Early real-world findings have shown that a well-conducted exposure notification app can have positive results. An early analysis of the implementation of a test and trace program, including an app, on the Isle of Wight showed a drop in transmissions. Meanwhile, a pilot study in Spain showed that an exposure notification app can be 80% more effective than manual contact tracing alone. 

Adoption and rollout strategies are a critical piece of a successful exposure notification app strategy. LFPH is providing consulting and materials to any PHA or development team working on exposure notification apps. If you’d like to discuss your rollout with us, please contact us.