It seems to not require an app. Apple calls this an App-less experience -- as if having an app was the still supported but the legacy way. In their description

It seems to not require an app. Apple calls this an App-less experience -- as if having an app was the still supported but the legacy way. In their description of "step 5" at the below link, users can enter an eight digit code or follow a url to inform their phone of an infection. https://developer.apple.com/documentation/exposurenotification/supporting_exposure_notifications_express https://developer.apple.com/documentation/exposurenotificati...