Safety and Immunogenicity of COVI-VAC, a Live Attenuated Vaccine Against COVID-19

Inclusion Criteria: * Subjects who meet all of the following criteria may be included in the study: 1. Men and women aged between 18 to 30 years of age, inclusive, on the day of signing the informed consent form (ICF) 2. In good health with no history, or current evidence, of clinically significant medical conditions with particular reference to, but not restricted to, hypertension, diabetes, thromboembolic disorders, coronary heart disease, chronic obstructive lung disease, and no clinically significant test abnormalities that will interfere with subject safety, as defined by medical history, physical examination, vital signs (including oxygen saturation), ECG, spirometry, and safety laboratory tests as determined by the Investigator 3. Total body weight of greater or equal to 50 kg and body mass index (BMI) greater or equal to 18.0 kg/m2 and less than or equal to 28.0 kg/m2 (the upper limit of the BMI may be increased to less than or equal to 30 kg/m2 at the Investigator's discretion in case of a muscular healthy subject for whom BMI may be biased upwards) 4. Negative drugs of abuse, cotinine, and alcohol screen (unless explained by prescribed medication) 5. Negative pregnancy test for women who have not been surgically sterilised 6. Negative COVID Clear test Exclusion Criteria: Subjects who meet any of the following criteria will be excluded from the study: 1. Haemoglobin A1c ≥6.0% or 42 mmol/mol 2. Forced expiratory volume in 1 second (FEV1) less than 80% predicted value 3. Signs or symptoms suggestive of upper or lower respiratory tract infection (including fever or persistent cough) within 28 days of Day 1 4. Pregnant, possibly pregnant, or lactating women 5. Women who have been pregnant through the third trimester or given birth within the past 6 months 6. Planning a pregnancy (subject or partner) within 90 days after the last IMP dose 7. Inadequate venous access for repeated phlebotomy 8. History of confirmed or suspected SARS-CoV-2 infection 9. Contact with any individual subsequently confirmed to have SARS-CoV-2 within 14 days after contact 10. History of wheeze treated with inhaler(s) 11. Respiratory symptoms, including wheeze, that have ever resulted in hospitalisation 12. Known bronchial hyperreactivity to viruses 13. Any significant abnormality altering the anatomy of the nose in a substantial way or nasopharynx that may interfere with the aims of the study and in particular any of the nasal assessments or viral challenge (historical nasal polyps can be included, but large nasal polyps causing current and significant symptoms and/or requiring regular treatments in the last month are excluded)