An analysis of 7 million contacts of COVID-19 patients in the United Kingdom estimates that most transmissions resulted from exposures lasting 1 hour to several days and that households accounted for 40% of spread from spring 2021 to early 2022.

A team led by University of Oxford researchers evaluated data from the National Health Service (NHS) COVID-19 contact-tracing smartphone app in England and Wales to estimate how well app measurements correlated with real-life transmissions.

Using Bluetooth signal strength and 240,000 positive COVID-19 tests, the NHS notified the contacts of confirmed patients of exposures from April 2021 to February 2022 and recorded data on whether contacts also tested positive. The results were published today in Nature.