A Clinical Trial Evaluating the Safety and Efficacy of AP1189 Versus Placebo as an add-on to Standard of Care in Participants With Respiratory Insufficiency Expected to be Caused by Infection With Respiratory Viruses

Inclusion Criteria: * Written informed consent has been obtained prior to initiating any study-specific procedures * Expected respiratory viral infection, and positive for either SARS-COV-2, Influenza A or B, or RSV as confirmed by a bedside LAF test, qualitative PCR, or quantitative PCR (Q-PCR). * Hospitalized with respiratory insufficiency expected to be caused by respiratory viral infection defined by SpO2 ≤ 93 % on ambient air or supplementary oxygen supply via nasal catheter or facial mask (WHO Clinical Progression Scale score 5 or 6). Or in participants with hypercapnic respiratory failure (usually due to COPD) the SpO2 threshold is SpO2 ≤ 85 %. * Duration of disease from first symptom\< 15 days before enrolment * Females of childbearing potential using reliable means of contraception or are post-menopausal or are surgically sterilized * Females of childbearing potential with a negative pregnancy test at screening and baseline * As the morbidity and mortality of respiratory infections are many fold increased in vulnerable participants, vulnerable participants are not excluded but included as subgroups. * Screened within 24 hours of hospital admission to the hospital, or within 24 hours of receiving a patient, if the patient is transferred from another hospital or another hospital department due to respiratory distress Exclusion Criteria: * In the investigator's opinion, progression to death is imminent and inevitable irrespective of the provision of treatment * Alrea…