The origin of the SARS-CoV-2 virus that causes COVID-19 remains a mystery and a major source of tension between China and the United States.
A joint study by China and the World Health Organization (WHO) this year all but ruled out the theory that COVID-19 originated in a laboratory, saying that the most likely hypothesis was that it infected humans naturally, probably via the wildlife trade.
A WHO-led team of experts spent four weeks in and around the central city of Wuhan with Chinese scientists and said in a joint report in March that the SARS-CoV-2 virus had probably been transmitted from bats to humans through another animal but that further research was needed.
