China’s decision to lock down the city of Wuhan, ground zero for the global COVID-19 pandemic, may have prevented more than 700,000 new cases by delaying the spread of the virus, researchers said Tuesday.

Drastic Chinese control measures in the first 50 days of the epidemic bought other cities across the country valuable time to prepare and install their own restrictions, according to the paper by researchers in China, the United States and the UK, published in the journal Science.

By day 50 of the epidemic — February 19 — there were 30,000 confirmed cases in China, said Oxford fellow Christopher Dye, one of the paper’s authors.

“Our analysis suggests that without the Wuhan travel ban and the national emergency response there would have been more than 700,000 confirmed COVID-19 cases outside of Wuhan by that date,” he was quoted as saying in a press release.

“China’s control measures appear to have worked by successfully breaking the chain of transmission — preventing contact between infectious and susceptible people.”

The researchers used a combination of case reports, public health information and mobile phone location tracking to investigate the spread of the virus.

The phone tracking provided a “fascinating” new stream of data, said another of the report’s authors, Penn State biology professor Ottar Bjornstad.

The time period they studied encompassed China’s biggest holiday, the Lunar New Year.