SHANGHAI: The northern Chinese city of Tianjin on Sunday advised its nearly 14 million people to stay home while it conducted mass Covid testing after a spate of recent cases, including two caused by the Omicron variant, state-controlled media reported. Tianjin emerged as a new area of concern after more than 20 Covid cases were reported there in the last few days, most of them imported from abroad, according to the National Health Commission. They include at least two cases of the Omicron variant, as well as 15 infections among elementary and middle school students, according to various state…