One afternoon in May, Michael Joseph Smith, a pediatric infectious disease specialist, strides in baseball-patterned socks through a Duke University facility in Durham, N.C., to welcome Cameron O’Hara, a 14-year-old vaccine trial subject. Smith has been acting as co-principal investigator at one of the sites that’s been testing the Pfizer-BioNTech vaccine in kids since last winter. O’Hara and his mother have come to the office following the “unblinding” process—in which he’d learned, to his disappointment, that he’s been getting a placebo—to get his first dose of the real thing. He crosses his sneakers and grips his mom’s hand as the needle goes into his arm.