1. 1RTI International, 3040 East Cornwallis Road, P.O. Box 12194, Research Triangle Park, North Carolina 27709
2. 2Division of Viral Diseases, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, Georgia 30329
3. 3Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson, South Carolina 29634, USA