The prevalence and phenotype of hepatitis B virus vaccine escape variants propagated by mother to child transmission in Indonesia. Hepatitis B virus (HBV) infection is a major cause of ill health and death worldwide. HBV can lead to can lead to cirrhosis, liver failure and liver cancer, and kills more than 780,000 people every year. Across the world 350 million people are chronically infected with the virus, with the majority (75%) occurring in Asia. HBV is therefore a major health and economic burden in Indonesia.   Transmission of HBV is through contact with HBV-infected blood, and can occur during blood transfusions, needle sharing and during childbirth. The prevalence of HBV infection is particularly high in south-east Asia, where mother-to-child transmission (MTCT) is the most common route of infection. Infection with the virus during childhood increases the risk of developing a chronic infection and the chances of developing severe disease and understanding how the virus transmits between mother and infant is therefore of upmost importance. Breaking the chain of mother-to-child transmission is an essential part of the global strategy to limit HBV infections. In Indonesia, universal vaccination of newborns has been introduced to help prevent transmission, but infection remains common in pre-school and school age children and urgent review of strategies to prevent MTCT is required. Current diagnostic tests look for the presence of viral proteins in the blood. However, 'false negative' results can occur in these diagnostic tests. Testing for the presence of the viral genome in infected patients is a far more sensitive way of screening for potential infections. Cheaper, more sensitive tests will need to be deployed in resource-poor countries to enable better clinical intervention. Improved screening and targeted intervention in those cases that are likely to transmit virus to a newborn child would make a major contribution to reduced incidence of chronic infection.   In this research project we aim to investigate the factors involved in MTCT of HBV. The first objective of the project is to screen large numbers of mothers who are likely to be infected with the virus, utilising routine diagnostic tests and high-sensitivity assays that detect the HBV genome. We will then screen for the presence of new infection in infants, both at time of birth and nine months later. In those mother-infant pairs that demonstrate MTCT we will sequence the viral genome using state-of-the-art sequencing techniques to determine if specific types of the virus are transmitted. We will also analyse the properties of the transmitted virus variants and see if they are resistant to current vaccines. We will furthermore establish if specific clinical interventions could be introduced that prevent transmission of these variants.  This research will determine if the current clinical tests do not detect all of the transmission events, and if there are better screening techniques that will permit targeted clinical intervention. The research findings have the potential to demonstrate if there are specific viral determinants of MTCT in areas of high prevalence of HBV infection, and if there are variants which escape vaccination. Taken together, this information has potential to improve the global healthcare management of HBV. The Newton Fund builds research and innovation partnerships with developing countries across the world to promote the economic development and social welfare of the partner countries.