A Phase II Randomized, Open-label, Multicenter, Dose-ranging Study in adults and pediatric individuals 12 years of age and older to assess the safety, immunogenicity, pharmacokinetics, and pharmacodynamics of AZD7442, a combination of two Monoclonal Antibodies (Tixagevimab and Cilgavimab), for pre-exposure prophylaxis (prevention) of COVID-19