Does America face a slowdown in economic growth?

IT WAS INEVITABLE that global economic growth would slow from the breakneck pace set as economies recovered from the pandemic. Lately, investors have begun to worry about something worse: that America’s economy, which has led the rich-world rebound, could decelerate sharply. As well as supply bottlenecks and the withdrawal of economic stimulus, the country, like many others, now faces the ultra-infectious Delta variant. A painful slowdown remains unlikely. But the renewed spread of the virus is the biggest of those three dangers.

To see how the latest rich-world coronavirus waves are likely to develop, consider that on July 20th America reported a seven-day moving average of 112 new cases for every million people. That is roughly where Britain, with a higher rate of vaccination, more restrictions and deadlier past outbreaks, was in mid-June before Delta got going. Britain now has 699 cases per million, the fifth-highest rate in the world. If all else is equal, Delta spreads two or three times as quickly as the original strain of the virus.

Thankfully, vaccines prevent almost all severe cases of disease and treatments have improved, saving more lives among those who are infected. That is why England lifted ...