Inclusion Criteria:  Age ≥18 years of age Able to give written informed consent Index cases: presenting with mild/moderate viral infection symptoms, who the Investigator considers can be treated at home. Negative pregnancy test for women of childbearing age at Baseline visit (includes screening). Able to operate and maintain nebuliser, as assessed by the Investigator.  Exclusion Criteria:  Both Index cases and Household members: Unable to tolerate use of a nebuliser for approximately 8-10 minutes as required by the study according to Investigator's opinion  Both Index and Household members:  Any unstable, uncontrolled or severe medical condition which in the opinion of the investigator would make the participant unsuitable for the trial COPD/Asthma or any severe respiratory disease requiring the use of oral steroids or biologics Participation in other clinical investigations utilising investigational treatment within the last 30 days / 5 half-lives whichever is longer Participant lives at home with no other potentially eligible adults in the household Women of childbearing age unable or unwilling to use an adequate form of contraception for the duration of the study i.e. double barrier contraceptives. Male participants who are unwilling or unable to use an effective method of contraception for the duration of the study. Known allergy/hypersensitivity to or relevant drug-drug interaction with study drug/components of study drug History of methaemoglobinaemia Deemed unlikely to be able to adhere to protocol in view of investigator Any subject who in the opinion of the investigator would not be best served by participating in this clinical trial Prescribed Nitric Oxide donating agents (e.g. Nitroprusside, Isosorbide dinitrate, Isosorbide mononitrate, Naproxcinod, Molsidomine and Linsidomine)