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