CROWN CORONATION: COVID-19 Research Outcomes Worldwide Network for CORONAvirus prevenTION

CROWN CORONATION is an international, Bayesian platform adaptive, randomized, placebo-controlled trial assessing the effectiveness of candidate interventions in preventing COVID-19 disease in adults. Randomization will be stratified by age (\<50 and ≥50) and site. Participants will be healthcare workers at risk of contracting SARS-CoV-2. Participants will be randomized into one of two arms: * Education and surveillance plus MR or MMR vaccine * Education and surveillance plus Placebo While the initial intervention to be tested on the platform will be the MR or MMR vaccine, other interventions might be added or removed over the course of the trial. The trial will evaluate which of the intervention arms is most effective at decreasing the incidence of symptomatic COVID-19 disease, without unacceptable side effects or safety events. All participants will require be required to have a mobile phone to participate. This is standard in all the countries in this study. Most, but not all, will also have a smartphone. Participants will complete weekly data logs via SMS texting. Follow-up information will be collected until approximately 5 months after the end of treatment or death. Participants who develop symptomatic COVID-19 during the last month of observation will at a minimum be followed-up until symptom resolution and at a maximum until 6 months after randomization (whichever comes first). Telemedicine approaches to collecting information on participants will be used where possible. The trial will provide adherence support interventions that have been shown in randomized controlled trials to improve adherence to Human Immunodeficiency Virus treatment and adapted for HIV Pre-Exposure Prophylaxis (HIV PrEP) (e.g. two-way SMS with check in for those that report symptoms or adverse events). The database will be hosted on UK-based servers which are expected to be managed by Sealed Envelope Ltd. Local investigators will have access to the part of the CRF to enable recording of outcome data and/or severity of COVID-19 symptoms. Participants will be given a secure login to enable them to complete an initial participant health questionnaire and the regular data logs. It is envisaged that these will be completed at least weekly.