Within a few years, Offit had partnered with several other scientists and begun to develop a rotavirus vaccine. Their oral immunization, called RotaTeq and delivered as a series of sugar-sweet drops to infants, would ultimately be licensed in 2006. Today, it remains one of the two main rotavirus vaccines available to American children. Offit is now a pediatrician at Children’s Hospital of Philadelphia, where, he told me, “most residents have never seen an inpatient with rotavirus-induced dehydration”—thanks in large part to the country’s deployment of rotavirus vaccines, which reaches about 70 percent of U.S. children each year.