This is a Phase 1a, single-country, single-centre, single-blinded, COV2 vaccine formulation randomized trial designed to investigate and compare the safety and immunogenicity of two COV2 vaccine formulations. COV2 is a nasal, investigational vaccine against COVID-19, based on a serotype 5 adenoviral vector producing modified SARS-CoV-2 spike protein.

Participants will receive one of the two COV2 formulations in two doses on Day 0 and Day 28.

This trial consists of two parts; Part 1 is a vaccination phase assessing safety and immunogenicity and Part 2 is a long-term immunogenicity follow-up assessing persistence of immune response.

Inclusion criteria

• Has voluntarily signed the written informed consent
• Male or female aged ≥18 to ≤75 years
• Good general health based upon the results of the medical history, laboratory tests, physical examination, ENT clinical examination, and vital signs as assessed by the investigator
• Prior vaccination with at least two doses of any COVID-19 vaccine with last dose obtained ≥180 days before the planned baseline (Day 0) visit
• Has a personal smartphone, tablet or computer with internet access, and is considered willing and able to report the data in the ePRO and to comply with the reporting timelines
• Willing and able to comply with the instructions to participants
• Not of childbearing potential or willing and able to use a highly effective contraception method consistently and correctly during the entire trial

Exclusion criteria

• Pregnant, planning to become pregnant, or breastfeeding women

• Received any investigational drug < 180 days prior baseline

• Antigen positivity or PCR confirmed SARS-CoV-2 infection less than 180 days apart from screening or during screening and/or baseline

• Any SARS-CoV vaccination was administrated < 180 days prior the planned baseline (Day 0) visit

• Any other vaccination within 60 days prior the planned baseline (Day 0) visit

• Administration of immunoglobulins or blood products within 90 days prior baseline

• Current use of immunosuppressant medication (except topical and inhaled steroids, which are permitted in indications not prohibited in the exclusion criteria)

• Use of steroid nasal sprays within 30 days prior to screening

• Use of any oral or nasal decongestants within 7 days prior to screening

• Any confirmed or suspected immunodeficient state

• Chronic respiratory diseases (except treatment -controlled asthma)

• Severe chronic cardiovascular and endocrinological diseases (e.g., medicine or insulin treated diabetes), liver and renal insufficiency or serious psychiatric diseases

  - Medication for elevated cholesterol or blood pressure or dietary treated diabetes or hypothyreosis are not exclusion criteria

• Any diagnosed disease or abnormality in the nasal or upper respiratory tract, such as acute/chronic rhinosinusitis; nasal polyposis; mucosal pathology or tumor of nasal cavity, pharynx or nasopharynx; significant obstructive nasal deformity; recurrent epistaxis; sleep apnea; anosmia

  - History of adenoidectomy and/or tonsillectomy are not exclusion criteria

• Severe obesity (BMI ≥ 35)

• Cancer treated within 5 years

• Known allergy/hypersensitivity to any ingredients of the COV2 vaccine

• Previous anaphylactic reaction

• Any clinically significant abnormal finding in the screening laboratory tests

• Inability to sign ICF or to understand and comply with trial related instructions and requirements

• Individuals who are employees of, or directly affiliated with, the sponsor, or site staff or their immediate family members.