Contact-tracing software could accurately gauge COVID-19 risk
Researchers found that the [NHS COVID-19 app in England and Wales] did, in fact, accurately translate the duration and proximity of a COVID-19 exposure to a relevant epidemiological risk score. The app assessed a contact’s risk by multiplying the length of contact, the proximity of contact, and the infectiousness of the index case as determined by how long it had been since the index case started showing symptoms or tested positive.