A new coronavirus outbreak in Beijing could have come from strains that originated in South Asia or Southeast Asia, according to a study by Harvard University researchers. The study, which has not been peer-reviewed, was based on the genetic sequencing data of three virus strains – two from patients in Beijing and the other from the environment – made public by the Chinese Centre for Disease Control and Prevention. Georg Hahn, a research associate with the Biostatistics Department of the Harvard T.H. Chan School of Public Health, and his team compared these genes to more than 7,000 whole-genome sequences reported from around the world. They found the three strains were part of a group that has been mostly circulating in Europe, but has recently been reported “almost exclusively” in Asia’s tropical zone. “The new cases in Beijing were reintroduced by transmissions from South(east) Asia” between April and June, Hahn and his colleagues said in a paper posted on preprint server bioRxiv.org on Tuesday. A cluster of new infections emerged in Beijing on June 11 after nearly two months without any cases. More than 7 million people have now been tested across the Chinese capital as part of efforts to control the outbreak, which has so far led to 326 cases – many of them linked to a wholesale food market. In Wuhan, where the new virus was first reported in December, the earliest cases were also linked to a food market. Wu Zunyou, chief scientist with the China CDC, said that similarity could be an important clue to the origin of the outbreak. Both cities had cases “concentrated in an area where seafood is sold”, he told the official China News Service on Monday. “Genetic sequencing showed the virus in Beijing could not have come from animals, nor was it derived from the strains that were prevalent earlier.” The China CDC said in a report last week that strains found in the latest Beijing outbreak were imported, and the virus could have been brought into the market by someone who was infected or through contaminated food products from overseas. Yang Peng, a researcher with the Beijing Centre for Diseases Prevention and Control, told local media their investigation had pointed “in the direction of Europe”. Coronavirus studies strengthen link between loss of smell or taste and Covid-19 But Wu Guizhen, head of the National Institute for Viral Disease Control and Prevention, said the strains found in Beijing had two “foreign mutations” – one that first emerged in Europe and the other that was first reported in Britain before it spread across Europe and America. Those mutations had been detected in China back in March, from travellers returning from overseas, Wu told official newspaper Science and Technology Daily on Friday. She added that the strains found in Beijing were genetically older than those circulating in Europe at present. Adding to the complication for investigators, China CDC director Gao Fu told Beijing Daily last month that the virus could have been present in the Beijing food market for one to two months before the outbreak. The virus is thought to prefer low temperatures, and Gao said it could have been “hiding” in the cold, damp, dark environment of the market. But according to a researcher with the Chinese Academy of Sciences, it was more likely that the outbreak was caused by a “fairly recent event, likely in June”. The researcher is part of a team that has analysed more than 60,000 genetic sequences of the virus in global databases. They found more than 200 virus strains were closely linked to the samples from Beijing. When will it end? The mirage of normal life in coronavirus-hit Chinese capital “That means they could have come from anywhere,” said the researcher, who requested anonymity because she was not authorised to speak to the media. And with a lack of adequate samples and sequencing available from many parts of the world, there was a “fairly good chance” the strains could have come from a place where there was no data, she said. The researcher said a conclusion could not be reached on the origin of the Beijing strains because “the cases in South Asia may have travelled from other areas”.