Exposure Notifications

The Google Apple Exposure Notification (GAEN) framework for privacy-preserving automated contact tracing.

Update: On Sep 18, 2023 Google & Apple decided to shut down exposure notifications. Learn more.

The Exposure Notifications System is a framework, jointly developed by Apple and Google, that uses Bluetooth Low Energy and privacy-preserving cryptography to enable public health authorities to build an opt-in exposure notification system. Apple launched this API on May 20, 2020 on iOS 13.5 and above. Google launched it on Android via Google Play Services so that devices as far back as Android Marshmallow can be supported.
Exposure Notifications

Worldwide Adoption

Google and Apple's policy restricted the use of GAEN to public health authorities only, meaning only public health authorities were allowed to develop and deploy apps that use the GAEN framework. As of May 22, 2023:

Exposure Notifications Worldwide

Adoption in United States

Google and Apple's policy restricted the use of GAEN to public health authorities only, meaning only public health authorities were allowed to develop and deploy apps that use the GAEN framework.

Exposure Notification Status United States

Risk Model

Similar to DP-3T and TCN protocols, the GAEN framework was built at the operating-system level, requiring neither a background process nor any special power or Bluetooth permissions. The framework is interoperable between Android and iOS devices and does not require downloading a dedicated app — a significant advantage over other protocols.

WeHealth Risk Model

The risk model computes Meaningful Exposure Minutes (MEM) by combining infectiousness curves, distance weights, report type weights, and MEM thresholds. Each of these parameters is configurable by Public Health Authorities to reflect local epidemiological conditions.

Efficacy
CDC Pennsylvania Exposure Notification Study

CDC Study: Estimated Cases Averted by COVID-19 Digital Exposure Notification, Pennsylvania

We combined field-based data with mathematical modeling to estimate that 7–69 cases were averted per 1,000 notifications sent during November 8, 2020 – January 2, 2021.

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WA Notify Cases Averted

Early Epidemiological Evidence of Public Health Value of WA Notify

Analysis of the first four months of implementation of Washington State's exposure notification system.

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New South Wales Australia Contact Tracing Study

Effectiveness Evaluation of Digital Contact Tracing in New South Wales, Australia

Study of app uptake and its contribution to the COVID-19 response in New South Wales, Australia.

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NHS COVID-19 App England and Wales Study

Epidemiological Impacts of the NHS COVID-19 App in England and Wales

About 1 million cases averted (sensitivity analysis: 450,000–1,400,000), 44,000 hospital cases, and 9,600 deaths prevented throughout the app's first year.

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MIT Lincoln Laboratory Contact Tracing Assessment

MIT Lincoln Laboratory: Automated Contact Tracing Assessment

Assessment of automated contact tracing conducted in partnership with the University of Arizona, including data collection methodology and technology evaluation.

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WeHealth Bermuda Delta Wave Impact

WeHealth's Impact during Delta Wave in Bermuda

Up to 20% case load reduction and preservation of approximately one week of economic activity during the Delta wave.

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University of Arizona Exposure Notification Pilot

How a Smartphone App and Contact Tracing Helped Keep UArizona Open

11% reduction in transmission rate (R(t)) and 47% adoption rate among infected users — demonstrating the effectiveness of exposure notification technology.

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