Funding for this research was provided by:
National Center for Global Health and Medicine (28S8, 25S1)
Japan Agency for Medical Research and Development
Received: 17 July 2018
Accepted: 21 October 2019
First Online: 8 November 2019
Ethics approval and consent to participate
: The study protocol was approved by the Ethical Committee of Bach Mai Hospital, Hanoi, Vietnam, decision number: 529 QD-BM on May 10, 2013 and the Ethical Committee of the National Center for Global Health and Medicine, Japan, decision number: 1496 on October 1, 2013. Before the collection of questionnaire data and venous blood samples, information sheets and consent forms were distributed to parents and students by the schools. Students participating in the study agreed to provide written informed consent with written approval from their parent(s). All participants could withdraw from the study at any time without any threats or disadvantages.
: Not applicable.
: The authors declare that they have no competing interests.