aVaccine and Infectious Disease Division, Fred Hutchinson Cancer Center

bDivision of Allergy and Infectious Disease, Department of Medicine, University of Washington

cPediatric Infectious Disease Division, Seattle Children's Hospital

dDepartment of Pediatrics, University of Washington, Seattle, Washington, USA

Correspondence to Jim Boonyaratanakornkit, 1100 Fairview Ave N, Mail Stop E5-320, Seattle, WA 98109, USA. Tel: +206 667 5000; e-mail: [email protected]