1. 1Department of Pediatrics, The University of Medicine and Pharmacy, Ho-Chi-Minh City, Vietnam
2. 2Department of Clinical Hematology, Children's Hospital No. 1, Ho-Chi-Minh City, Vietnam
3. 3Department of Clinical Hematology, Children's Hospital No. 2, Ho-Chi-Minh City, Vietnam
4. 4Department of Public Health, Fukushima Medical University, Fukushima, Japan
5. 5Department of Epidemiology and Preventive Medicine, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan