1. University of Pennsylvania, Wistar Institute, 4650 Wismer Road, Doylestown, PA 18901, USA
2. Laboratory of Virology, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
3. Aventis Pasteur–Merck, SharPe & Dohme, Public Affairs, 8 rue Jonas Salk, F–69007 Lyon, France
4. Faculty of Medicine, University of Louvain, 50 Avenue Mourner, B–1200, Belgium
5. GlaxoSmithkline, One Franklin Plaza, Philadelphia, PA 19102, USA
6. Rega Institute, Faculteit Geneeskunde, Katholieke Universiteit Leuven, Minderbroederstraat 10, Leuven, Belgium