Study to Evaluate a Single Dose of LTX-109 in Subjects With COVID-19 (Coronavirus Disease 2019) Infection.

Inclusion Criteria: 1. Willing and able to give electronically signed informed consent for participation in the study. 2. Male or female subject ≥18 years of age at screening. 3. Women of child-bearing potential have to agree to use an acceptable birth control method during participation in the investigation and a negative pregnancy test (beta human chorionic gonadotropin dipstick test in urine) at Day 1 will be required. 4. A positive PCR test (polymerase chain reaction test) or antigen test for SARS-CoV-2. The positive result must be available no later than 4 days from initiation of symptoms, if any. 5. Duration of symptoms not exceeding 6 days prior to baseline/IMP administration (Day 1). 6. Access to a mobile phone or computer and ability to use the electronic diary application and to participate in web-based appointments. Exclusion Criteria: 1. History of any clinically significant disease or disorder which, in the opinion of the Investigator, may either put the subject at risk because of participation in the study, or influence the results or the subject's ability to participate in the study. 2. Other upper respiratory tract infection with concomitant symptoms that can influence the results, such as sinusitis or tonsillitis. 3. Known allergy or hypersensitivity to the components of the IMP. 4. Current use of immunosuppressive therapy within the last 4 weeks prior to Day 1 and during the study. 5. Current use of nasally administered drugs within the last 2 weeks prior to Day 1 and during the study. 6. Vaccinated against COVID-19 or scheduled for vaccination within the study period. 7. Previous COVID-19 infection. 8. Any systemic anti-viral treatment within the last 4 weeks prior to Day 1 and during the study. 9. Pregnant, nursing or actively trying to conceive a child. 10. Inability to take medications nasally. 11. In situ nasal jewellery or open nasal piercings. 12. Planned treatment or treatment with another investigational drug within 30 days prior to Day 1. Subjects consented and screened but not dosed in previous Phase I studies are not excluded. 13. Investigator considers the subject unlikely to comply with study procedures, restrictions and requirements.