Despite the rather short history of vaccination, compared with the millennia of various human plagues and pestilences, more than a dozen major infectious diseases (most notably, smallpox, poliomyelitis, rabies, diphtheria, tetanus, pertussis, Haemophilus influenzae type b disease, measles, mumps, and rubella) have been controlled in many parts of the world [1]. The recently licensed rotavirus vaccines show great promise in this new century for controlling an infection which leads to 25,000–50,000 hospitalizations, nearly 400,000 emergency room visits, and 400,000 medical care visits of children in the United States annually, while at the same time leading to nearly 600,000 deaths worldwide [2–5].