Xi'an is about 900 km (560 miles) from China's Olympics venues - Copyright AFP/File RODGER BOSCH The Chinese city of Xi’an, where 13 million residents are currently confined to their homes, announced tightened restrictions on Sunday as the country recorded its biggest Covid-19 infection numbers in 21 months. China has stuck to a “zero-Covid” strategy involving tight border restrictions, lengthy quarantines and targeted lockdowns. Authorities have been especially vigilant in recent months to avoid an outbreak before February’s Beijing Winter Olympics, but there have been sporadic flare-ups. But on Sunday the country reported 206 new Covid infections — the highest...