1. *Infectious Diseases Division, Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305;
2. †Department of Health and Human Services, Division of Viral Products, Office of Vaccine Research and Review, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, MD 20867; and
3. ‡Department of Pediatrics, Palo Alto Medical Foundation, Palo Alto, CA 94301