After the first local Omicron cases in China were detected, the country’s north-eastern city of Tianjin has ordered mass testing for its entire population. The authorities confirmed Sunday that 20 Covid-19 infections had been detected in the city since Friday. Sequencing had shown that the first two of them were the fast-spreading Omicron variant. China’s state news agency Xinhua reported that the remaining 18 infections stood in connection to those Omicron cases, most of them school children and their family members. The authorities expect the case count to climb following the mass testing. T…