If the two countries had followed the same strategy, Sweden’s demographic and institutional advantages should have led to a Covid-19 mortality rate significantly lower than America’s. In fact, Sweden’s mortality rate is about 30% higher than the U.S. rate, and America doesn’t have a low rate by the standards of highly developed societies. Swedish officials have conceded that their country has failed to protect its elderly citizens. If the U.S. had adopted Sweden’s approach and experienced Sweden’s death rate, 30,000 Americans who are alive today, many of them parents and grandparents, would have perished.

Until recently, Sweden’s defenders had a rejoinder: Countries with mandatory lockdowns are only postponing the inevitable. Because a higher fraction of Sweden’s population had become infected, it would reach “herd immunity” much faster than other countries, whose death rates would catch up. In April, the country’s chief epidemiologist, Anders Tegnell, cited estimates that Stockholm had probably achieved an immunity rate of 15% to 20%, and the Swedish Public Health Agency projected that one-third of Stockholmers would be infected by May 1.

But when tests were conducted, it turned out only 7.3% of Stockholm residents had contracted the disease and developed antibodies against it by late April.