Bloomberg The rise of the highly-contagious delta variant is challenging even the most aggressive COVID-19 containment regimes, an ominous sign as economies look to open up and return to pre-pandemic life. An outbreak that started at an airport in the eastern Chinese city of Nanjing is testing that country’s zero-tolerance measures, which are some of the most sweeping and comprehensive in the world. New infections are rising by the dozens and seeding subsequent clusters around China despite well-honed systems of mass testing and stringent quarantines. Beijing reported its first locally transmitted infection in six months Thursday, linked to an outbreak in the southern province of Hunan among people who’d recently been to Nanjing.