Vaccine Preventable Disease Seroprevalence in a Nationwide Assessment of Timor-Leste (VASINA-TL): study protocol for a population-representative cross-sectional serosurvey.

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 1 year of age. Serum samples will be collected by phlebotomy and analysed for measles IgG, rubella IgG, SARS-CoV-2 antispike protein IgG, hepatitis B surface antibody and hepatitis B core antigen using commercially available chemiluminescent immunoassays or ELISA. In addition to crude prevalence estimates and to account for differences in Timor-Leste's age structure, stratified age-standardised prevalence estimates will be calculated, 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 seroepidemiology 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's 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.

The epidemiology of the COVID-19 pandemic in the small, low-resource country of Timor-Leste, January 2020 - June 2022.

Abstract: Timor-Leste, a small, mountainous half-island nation which shares a land border with Indonesia and which is 550 km from Australia, has a population of 1.3 million and achieved independence for the second time in 2002. It is one of the poorest nations in Asia. In response to the global coronavirus disease 2019 (COVID-19) pandemic, the Timor-Leste Ministry of Health undertook surveillance and contact tracing activities on all notified COVID-19 cases. Between 1 January 2020 and 30 June 2022, there were 22,957 cases of COVID-19 notified which occurred in three waves, the first which was delayed until April 2021 (community transmission of B.1.466.2 variant following major flooding), followed by waves in August 2021 (B.1.617.2 Delta variant transmission) and February 2022 (B.1.1.529 Omicron variant transmission). There were 753 people hospitalised due to COVID-19 and 133 deaths. Of the 133 deaths, 122 (92%) were considered not fully vaccinated (< 2 COVID-19 vaccines) and none had received boosters. Timor-Leste implemented measures to control COVID-19, including: rapid closure of international borders; isolation of cases; quarantining of international arrivals and close contacts; restrictions on internal travel; social and physical distancing; and, finally, a country-wide vaccination program. The health system's capacity was never exceeded.