Europe’s second wave built slowly, starting in midsummer. At that time, charts comparing coronavirus cases in America and Europe highlighted the inadequacy of the U.S. response; there were days on which individual American states recorded more new infections than the entire European continent. But in July, cases in Spain started to tick upward, and in August the numbers in France began rising. By September, Spanish covid-19 deaths had increased by a factor of ten, and France, for the first time, had recorded more than ten thousand new coronavirus cases in a single day. “We do have a very serious situation unfolding before us,” Hans Kluge, the W.H.O. regional director for Europe, warned. Spikes soon followed in the U.K., Italy, Germany, and other countries. The virus, once confined to a few hotspots, was everywhere.