In the minds of many, the halt of the Johnson & Johnson vaccine in April delivered doubt just as the mass COVID-19 vaccinations were making progress. There are three vaccines authorized for use in the United States, but Johnson & Johnson’s was a particularly important one, partly because its one-shot dose made it seem as though we might achieve herd immunity faster. Then, the government recommended pausing the company’s vaccine after six women who received it developed rare blood clots—and one woman died.