Duncan Clark’s flight was rolling down the runway in Paris in late October when President Emmanuel Macron announced a second national lockdown in France. The country had nearly 50,000 new Covid-19 infections that day. The United States had almost 100,000.He sighed with relief. He was headed to China. That day, it had reported 25 new infections, all but one originating abroad.Mr. Clark, a businessman and author, returned to China after spending nine months in the United States and France, his longest time away from the country since he moved to Beijing in 1994. He had been spending more time outside China …
