1Department of Child, Adolescent Health and Maternal Care, School of Public Health, Capital Medical University, Beijing, China;

2Department of Microbiology of Infectious Diseases, Yale School of Public Health, and Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, Connecticut, USA;

3Department of Hematology, Beijing Friendship Hospital, Capital Medical University, Beijing, China;

4UNESCO Chair on Global Health and Education, Peking University, Beijing, China;

5Beijing Key Laboratory of Environmental Toxicology, Capital Medical University, Beijing, China.

Correspondence: Yifei Hu, PhD. E-mail: [email protected]. Dayong Huang, PhD. E-mail: [email protected].