After teaching for three years at an international school in Shanghai, Michael is preparing to break his contract and leave, worn down by stringent measures against Covid-19.

Following two years of nearly-shut borders, onerous health checks and quarantine norms, a decision at the beginning of April to lock down China’s commercial centre proved the last straw for the 35-year-old.

"It has reached a point where the economic benefits of working here don’t make up for the lack of freedom to come and go," the science teacher said, declining to give his full name for reasons of privacy.

Michael is one of...