This is a single-centre, open-label, first-in-human, single ascending dose and multiple dose study to assess the safety, reactogenicity, and immunogenicity of the SC-Ad6-1 investigational product when administered via the intramuscular (IM), intranasal (IN) or inhaled (IH) route in healthy volunteers.

Key Inclusion Criteria:

• Adult males and females, 18 to 60 years of age (inclusive)
• Body mass index ≥ 18.0 and ≤ 32.0 kg/m2, with a body weight ≥ 50 kg at screening
• Must have been fully vaccinated against COVID-19 and received last dose not less than 3 months prior to Day 1 (High Dose #3 I.M. and I.N. booster arms only), not less than 5 months prior to Day 1 (High Dose #4 I.N. booster arm only) and not less than 12 months prior to Day 1 (I.H. booster arms and I.N or I.H. multiple dose booster arms only)

Key Exclusion Criteria:

• History or presence of significant cardiovascular, pulmonary, hepatic, renal, haematological, gastrointestinal, endocrine, immunologic, dermatologic or neurological disease
• History of chronic respiratory disorders including asthma, emphysema, interstitial lung disease, pulmonary hypertension, recurrent pneumonia, or recent (≤14 days prior to Screening) or ongoing respiratory tract infection
• History of thrombosis (e.g., deep vein thrombosis, pulmonary embolism, etc.), any coagulation dysregulation disorder, or a history of thrombosis noted in immediate family members
• History of any neurological disorders or seizures including Guillain-Barre syndrome, with the exception of febrile seizures during childhood
• Known previous infection with SARS-CoV-2 or presence of antibodies against SARS-CoV-2 or a positive SARS-CoV-2 PCR test (non-booster arms only)
• Any history of malignant disease ≤5 years prior to registration
• History of clinically relevant immunosuppression from, but not limited to, immunodeficiency conditions such as common variable hypogammaglobulinemia