Geneva: The United States and Britain are stepping up calls for the World Health Organisation to take a deeper look into the possible origins of Covid-19, including a new visit to China where the first human infections were detected. WHO and Chinese experts issued a first report in March that laid out four hypotheses about how the pandemic emerged. The joint team said the most likely scenario was that the coronavirus jumped into people from bats via an intermediary animal, and the prospect that it erupted from a laboratory was deemed “extremely unlikely”.