Inclusion Criteria:  Present to the general physician (GP)/specialist outpatient settings/respiratory clinics or in Emergency department (ED) settings with symptoms suggestive of a diagnosis of Acute Respiratory Infections (ARI) For inclusion in the home-based follow-up phases, must test positive for respiratory syncytial virus (RSV) and/or influenza and/or Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) per a molecular-based diagnostic assay (polymerase chain reaction [PCR]-based) using a nasal swab (nasopharyngeal or similar) sample. Co-infections are permitted to be enrolled in the study Must be able to read, understand, and complete questionnaires Must be willing to provide verifiable identification, has means to be contacted and to contact the investigator during the study Willing and able to adhere to the specifications in this protocol  Exclusion Criteria:  Has a clinical condition other than those as specified in study protocol which, in the opinion of the investigator, could prevent, confound, or limit the protocol-specified assessments Received an investigational drug (including investigational vaccines) within 3 months before the start of the study or the first data collection time-point Is currently enrolled or plans to participate in another investigational study on RSV, influenza or SARS-CoV-2 during the current study Is, in the opinion of the investigator, unlikely to adhere to the requirements of the study, or is unlikely to complete the full course of observation Cannot communicate reliably with the investigator