1. R. I. Glass and J. R. Gentsch are in the Gastroenteritis Section, Division of Viral and Rickettsial Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
2. R. I. Glass is currently on assignment to the Global Programme on Vaccines and Immunizations, World Health Organization, Geneva 27, Switzerland, CH-1211.
3. B. Ivanoff is in the Vaccine Research and Development Division, Global Programme on Vaccines, World Health Organization, Geneva, Switzerland.