Funding for this research was provided by:
Norwegian Research Council (Internal funding)
Received: 7 May 2019
Accepted: 24 December 2019
First Online: 5 February 2020
Ethics approval and consent to participate
: The study was ethically approved by the Hanoi University of Public Health (IRB No. 289/2016/YTCC-HD3). Written consent forms in the local language were also obtained from the participants. The consent to participate was verbally arranged by a project team from Hanoi University of Public Health.
: Not applicable.
: The authors declare that they have no competing interests.