1. Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia
2. Department of Microbiology, Mount Sinai School of Medicine, New York, New York
3. Department of Virology, University of Freiburg, Freiburg, Germany
4. Southeast Poultry Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Athens, Georgia