A strain of Covid-19 that has infected more than 300 people in Beijing since early June could have originated in South or Southeast Asia, according to a study by Harvard University researchers.

The virus found in Beijing cases is an imported strain of Covid-19, according to the China Centre for Disease Control and Prevention.

The Harvard study, published on the preprint website medRxiv.org on Tuesday and which has still to be peer-reviewed, took three of the SARS-CoV-2 genome sequences collected in Beijing last month and compared them to 7,643 samples worldwide.

“As the most recent cases in these branches are almost exclusively from South(east) Asia, this could suggest that the new cases in Beijing were re-introduced by transmissions from South(east) Asia,” they wrote.