The official corona warning app for Android and iOS has already adapted the risk calculation several times since the start to orient itself more optimally to the different virus variants.
The calculation of your individual infection risk is based on the following factors:
- Duration of encounter with a (later positive tested) person
- Distance in the encounter
- Time that has passed since the encounter
- Infectosity (derived from information when and whether the symptoms have used)
Corona warning apps for Android & iOS:
- Corona warning app for Android: inform now at chip and download it to the Google Play Store
- Corona warning app for iPhone: inform now at chip and download the Apple App Store
If the risk value determined therefrom exceeds the threshold value given by the Robert Koch Institut, users receive a notification of an increased risk of infection.
For some time now version 2.0 of the Exposure Notification Frameworks will be used by Apple / Google (also known as ExposureWindow mode of Google). The data of this interface serves as the basis for calculating the individual risk.
While in the first version 1.0 of the interface, averages of attenuation for all encounters with another device has been used in the course of the day, the consideration is currently for 30 minutes of time.
Since Bluetooth technology in smartphones is not designed to determine exact distances between multiple people in the near range, the removal according to the documentation of the Corona Warn app is calculated by the attenuation of the Bluetooth signal. At a distance of 8 meters, for example, a signal attenuation of about 73 dB is based on.
In order to be considered as a counted person contact in the Corona Warn app, must:
- For at least 5 minutes within the 30-minute window, the signal attenuation below 79dB
- The Transmission Risk Level should be at least 3. It is determined when sharing the diagnostic keys per day according to defined criteria such as symptom status and / or symptom start. Details can be found on the GitHub page of the Corona Warning App project.
If these criteria are not met, no count is within the app. It is a “non-risk encounter”. Although these encounters are counted in the contact protocol of the operating system, they are not included in the risk calculation of the app.
If the conditions are fulfilled, a weighting of the contact times, depending on the signal attenuation:
* Times with a damping <63dB are weighted with 80 percent.
* Times with a damping> = 63dB and <73dB are weighted at 100 percent.
* Times with a damping> = 73dB and <79dB are weighted with 10 percent.
Based on the Transmission Risk Level (3 to 8), a factor is determined between 0.6 and 1.6. With this factor, the weichte time is multiplied by the previous step, resulting in the normalized contact time. Finally, all normalized contact times are summed up. Ultimately, this means: Multiple short-risk encounters can lead to a red status in total. Based on this sum of normalized contact times, the final risk status is now determined:
- Sum of contact times less than 5 minutes: non-risk encounter (s) (green)
- Sum of contact times at least 5 minutes and less than 9 minutes: encounter (s) with low risk (green)
- Sum of contact times of at least 9 minutes: Encounter (s) with high risk (red)