Back to the days of the Silk Road, infectious diseases had traveled east to west across Eurasia. In earlier times, the spread had been limited by the slow pace of travel. In the age of sail, those who carried diseases tended to die en route. In 2020 the coronavirus moved at the speed of the jet and the high-speed train. Wuhan in 2020 was an affluent metropolis of recent migrants. Half the population would leave the city to celebrate Chinese New Year. SARS-CoV-2 took only a matter of weeks to spread from Wuhan around China and to much of the rest of the world.
