In the fall of 1998, rotavirus, a leading cause of severe childhood diarrhea, seemed ready to go the way of measles and rubella, viral diseases largely defeated by the administration of childhood vaccines. Wyeth had just had its RotaShield vaccine approved by the U.S. Food and Drug Administration (FDA), and it was poised to begin hastening the virus's decline.

Rotavirus is a worldwide affliction: almost every child is exposed to it by age five. Every year in the United States, 50,000 people (mostly children) are hospitalized with rotavirus-induced diarrhea and dehydration, and between 20 and 40 die. In poor countries the picture is much more grim. Of two million deaths attributable to diarrhea worldwide each year, over half a million are caused by rotavirus. A successful rotavirus vaccine would make an enormous impact on world health.