Inclusion Criteria:  Hospitalized Adults 18 year or older Moderately severe disease (CRB65 ≤ 2 at time of inclusion) Nasopharyngeal swab positive for influenza virus, parainfluenza virus, respiratory syncytial virus (RSV) or human metapneumovirus (hMPV) On antibiotic therapy as instituted by the receiving physician from the emergency department Signed informed consent must be obtained and documented according to ICH GCP, and national/local regulations.  Exclusion Criteria:  Requiring ICU admission at screening Requiring high-flow oxygen therapy or non-invasive ventilation at screening Signs of severe pneumonia (abscesses, massive pleural effusion, a well-defined lobar infiltrate on chest X-ray strongly suggestive of bacterial etiology) Not immunocompetent (i.e. on active chemotherapy, corticosteroid therapy equaling ≥ 20 mg prednisolone daily for ≥ 4 weeks, chronic immunosuppression due to solid organ transplant) SARS-CoV-2 positive Bacteremia Urine antigen test positive for legionella Any other infection necessitating antibiotic treatment Antibiotic use for assumed airway infection within the last 24 hours before admission to hospital