COVID-19 strain in Beijing outbreak may have come from Southeast Asia: Study

A new coronavirus outbreak Beijing that has infected more than 300 people since early June could have originated in South or Southeast Asia, according to a study by Harvard University researchers.

According to the China Centre for Disease Control and Prevention, the study is based the genetic sequencing of three virus strains and it shows that the virus found in Beijing cases is an imported strain of COVID-19.

Also read: Swine flu strain with 'human pandemic potential' found increasingly in China

7,643 samples from across the world were compared with these genes by Georg Hahn, a research associate with the Biostatistics Department of the Harvard T.H. Chan School of Public Health, and his team.

The Harvard study was published on the preprint website medRxiv.org on Wednesday and still has to be peer-reviewed.

The three genomes showed the greatest resemblance to cases in Europe from February to May, and to cases in South and Southeast Asia from May to June.

Also read: Beijing's Xinfadi market in focus after virus reportedly detected on salmon chopping boards

They were also similar to a small number of infections seen in China in March, suggesting the strain could have appeared first in China and then returned to the country three months later, the authors said.

"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.

The outbreak traced to Beijing's huge Xinfadi wholesale market on June 11 had infected 329 people by the end of Wednesday.

Quarantine restrictions and large-scale testing of residents began soon after the first cases were identified, and China also required all shipments of imported meat to be tested for COVID-19 before they could leave its ports.

The study comes amid the emergence of a swine flu strain with ''human pandemic potential'' found increasingly in Chinese slaughterhouses and can grow and multiply in the cells lining human airways.

The SARS-CoV-2 virus was believed to have originated in a market in the central Chinese city of Wuhan in December last year and has now infected more than 10 million people and killed more than 500,000 worldwide.

However, some studies suggest it could have been circulating much earlier after crossing the species barrier from horseshoe bats native not only to southwest China, but also Laos and Myanmar.