Vaccine Preventable Disease Seroprevalence In a Nationwide Assessment of Timor-Leste (VASINA-TL) - study protocol for a population-representative cross-sectional serosurvey
Authors: Arkell Paul , Sheridan Sarah L , Martins Nelson , Tanesi Maria Y , Gomes Nelia , Amaral Salvador , Oakley Tessa , Solano Vanessa , David Michael , Draper Anthony DK , Sarmento Nevio , Silva Endang da , Alves Lucsendar , Freitas Carlito , de Neri Machado Filipe , Gusmão Celia A , Costa Barreto Ismael da , Fancourt Nicholas SS , Macartney Kristine , Yan Jennifer , Francis Joshua R 
Published: December 2022

Introduction

Historic disruption in health infrastructure combined with data from a recent vaccine coverage survey suggests there are likely significant immunity gaps to vaccine preventable diseases and high risk of outbreaks in Timor-Leste. Community-based serological surveillance is an important tool to augment understanding of population-level immunity achieved through vaccine coverage and/or derived from prior infection.

Methods and analysis

This national population-representative serosurvey will take a three-stage cluster sample and aims to include 5600 individuals above one year of age. Serum samples will be collected by phlebotomy and analysed for measles immunoglobulin G (IgG), rubella IgG, severe acute respiratory syndrome coronavirus-2 anti-spike protein IgG, hepatitis B surface antibody and hepatitis B core antigen using commercially available chemiluminescent immunoassays or enzyme-linked immunosorbent assays. In addition to crude prevalence estimates and to account for differences in Timor-Leste’s age structure, we will calculate stratified age-standardised prevalence estimates, using Asia in 2013 as the standard population. Additionally, this survey will derive a national asset of serum and dried blood spot samples which can be used for further investigation of infectious disease sero-epidemiology and/or validation of existing and novel serological assays for infectious diseases.

Ethics and dissemination

Ethical approval has been obtained from the Research Ethics and Technical Committee of the Instituto Nacional da Saúde,Timor-Leste and the Human Research Ethics Committee of the Northern Territory Department of Health and Menzies School of Health Research, Australia. Co-designing this study with Timor-Leste Ministry-of-Health and other relevant partner organisations will allow immediate translation of findings into public health policy (which may include changes to routine immunisation service delivery and/or plans for supplementary immunisation activities).

STRENGTHS AND LIMITATIONS OF THIS STUDY

This project is one of very few large-scale, community-based, population-representative serosurveys to be conducted in low-middle income countries.

It will provide accurate seroprevalence estimates for multiple vaccine-preventable diseases, which will immediately inform public health policy and support an ongoing programme of vaccine research in Timor-Leste and the surrounding region.

A national asset of bio-banked serum samples will be derived, which can be used in cross-sectional and prospective studies of infectious disease epidemiology, including those which evaluate disease control interventions.

Diverse, remote communities across Timor-Leste will be visited, with primary sample analysis occurring at the National Health Laboratory in Timor-Leste. Therefore, fieldwork and laboratory-related logistical challenges will need to be overcome.