1. Zentrum für Infektionsforschung, Universität Würzburg, 97070 Würzburg, Germany1;
2. University of Missouri, Columbia, Missouri2;
3. Wyeth-Lederle Vaccines, West Henrietta, New York 14586-97283; and
4. Department of Paediatrics, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom4