ShigETEC Vaccine Study in Bangladesh

The goal of this clinical trial is to test ShigETEC vaccine, a combination vaccine against Shigella and ETEC diarrhoea in Bangladeshi adults (aged 18-45 years) and paediatric participants of three different age groups (aged 2-5 years, 12-23 months and 6-11 months). The main question\[s\] it aims to answer are: * Safety and clinical tolerability of the vaccine * Immune responses generated by the vaccine In the age-descending dose-escalating study * Adult participants will be divided into 2 escalating dose cohorts * Each age group of paediatric participants will be divided into 3 escalating dose cohorts * Participants in each cohort will receive three doses of vaccine/placebo two weeks apart * Solicited and unsolicited adverse events (AE) and serious adverse events (SAE) will be monitored after each vaccination dose * Stool samples will be collected for immunological analysis and shedding of vaccine strain * Blood samples will be collected for immunological analysis