1. Viral Vaccine Preventable Diseases Branch, Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
2. Department of Pediatrics, University of Colorado Denver School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA
3. Department of Medicine, University of Colorado Denver School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA
4. Department of Pathology, University of Colorado Denver School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA