An Adaptive Phase 3, Randomized, Double-blind, Placebo-controlled Study Assessing Efficacy and Safety of Sarilumab for Hospitalized Patients With COVID19

Primary Objective: To evaluate the clinical efficacy of sarilumab relative to the control arm in adult participants hospitalized with severe or critical Coronavirus Disease 2019 (COVID-19). Secondary Objectives: * Evaluate the 28-day survival rate. * Evaluate the clinical efficacy of sarilumab compared to the control arm by clinical severity. * Evaluate changes in the National Early Warning Score 2. * Evaluate the duration of predefined symptoms and signs (if applicable). * Evaluate the duration of supplemental oxygen dependency (if applicable). * Evaluate the incidence of new mechanical ventilation use during the study. * Evaluate the duration of new mechanical ventilation use during the Study. * Evaluate the proportion of participants requiring rescue medication during the 28-day period. * Evaluate need for admission into intensive care unit. * Evaluate duration of hospitalization (days). * The secondary safety objectives of the study were to evaluate the safety of sarilumab through hospitalization (up to Day 29 if participant was still hospitalized) compared to the control arm as assessed by incidence of: * Serious adverse events. * Major or opportunistic bacterial or fungal infections in participants with grade 4 neutropenia. * Grade greater than or equal to (\>=) 2 infusion related reactions. * Grade \>=2 hypersensitivity reactions. * Increase in alanine transaminase (ALT) \>=3X upper limit of normal (ULN) (for participants with normal baseline) or greater than 3X ULN AND at least 2-fold increase from baseline value (for participants with abnormal baseline). * Major or opportunistic bacterial or fungal infections.