As Covid-19 infections and deaths in the European Union eclipse those in the U.S., the region is confronting an ugly reality: Defeating the Delta variant is proving harder than a virus-weary continent had hoped.

Fast-rising Covid-19 contagion in parts of Europe, including Germany, is sparking fears of another winter of full hospitals. Countries are rushing to roll out booster shots as evidence accumulates that last summer’s vaccinations are losing some of their efficacy.