1 Oxford University Clinical Research Unit (OUCRU), Ho Chi Minh City 700000, Vietnam; Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7BN, UK. Electronic address: sayem.ahmed@ndm.ox.ac.uk.
2 Health Economics and Policy Unit, School of Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; Health Economics and Policy Research Group, Department of Learning, Informatics, Management, and Ethics (LIME), Karolinska Institutet Solna Campus, Solna, Sweden.