Covid-19 cases in slot Liverpool dropped by 21% compared with other areas during a mass testing pilot in Liverpool, research has shown.
People living or working in the city were offered tests whether or not they had symptoms from November to April.
More than 3,200 staff days among key workers were saved from being lost to quarantine through a test-to-release scheme, scientists say.
University of Liverpool's Prof Calum Semple says the pilot has been "incredibly valuable" for future scenarios.
Liverpool had one of the highest infection rates in England when the city-wide testing scheme began in November.
The speed at which lateral flow results were available, compared to PCR tests which are analysed in labs, saved about a day in the time it takes to identify someone as likely to pass on the virus, scientists say.
However, the study shows people living in deprived areas were less likely to take up testing.