Inclusion Criteria:

1. An informed consent form (ICF) has been signed and dated by the participant, an
investigator, and a witness

2. Adults age between 21 and 30 years inclusive (at the time of consent)

3. Evidence of having had a complete primary COVID-19 vaccination course as recommended
by the Ministry of Health*, with the last vaccination at least 14 days before
enrolment

4. Sero-suitable based on the pre-screening serology result 5a) Female participants
must be willing and able to use contraception from 2 weeks before the scheduled date
of viral challenge until 6 months after receipt of the final dose of study virus.
Negative urine pregnancy tests will be required at screening, and on admission to
the quarantine unit a negative serum beta human chorionic gonadotropin (β-hCG) is
required prior to inoculation.

5b) Male participants who are willing to use one of the contraception methods described
in the study protocol, from the time of the date of viral challenge, for 6 months.

6) In good health with no history of clinically significant medical conditions (as
described in Exclusion criteria) that would interfere with subject safety, as
defined by medical history, physical examination and routine laboratory tests, ECG,
and Chest X-Ray and determined by the Investigator at an admission evaluation.

7) Willing and able to commit to participation in the study.

Exclusion Criteria:

1. History or evidence of any clinically significant or currently active
cardiovascular, (including thromboembolic events), respiratory, dermatological,
gastrointestinal, endocrine, haematological, hepatic, immunological,
rheumatological, metabolic, urological, renal, neurological, psychiatric illness.
Specifically:

1. Participants with any history of physician diagnosed and/or objective test
confirmed asthma, chronic obstructive pulmonary disease, pulmonary
hypertension, reactive airway disease, or chronic lung condition of any
aetiology or who have experienced:

- Significant/severe wheeze in the past

- Respiratory symptoms including wheeze which has ever resulted in
hospitalisation

- Known bronchial hyperreactivity to viruses

2. History of thromboembolic, cardiovascular or cerebrovascular disease

3. History or evidence of diabetes mellitus

4. Any concurrent serious illness including history of malignancy that could
interfere with the aims of the study or a participant completing the study.
Basal cell carcinoma within 5 years of treatment or with evidence of recurrence
is also an exclusion

5. Migraine with associated neurological symptoms such as hemiplegia or vision
loss. Cluster headache/migraine or prophylactic treatment for migraine

6. History or evidence of autoimmune disease or known immunodeficiency of any
cause.

7. Other major disease that, in the opinion of the Investigator, could interfere
with a participant completing the study and necessary investigations.

2. Any significant abnormality altering the anatomy or function of the nose or
nasopharynx in a substantial way (including loss of or alterations in smell or
taste), a clinically significant history of epistaxis (large nosebleeds) within the
last 3 months, nasal or sinus surgery within 6 months of inoculation.

3. Clinically active rhinitis (including hay fever) or history of moderate to severe
rhinitis, or history of seasonal allergic rhinitis likely to be active at the time
of inclusion into the study and/or requiring regular nasal corticosteroids on an at
least weekly basis, within 30 days of admission to quarantine.

4. History of anaphylaxis and/or a history of severe allergic reaction or significant
intolerance to any food or drug, as assessed by the PI.

5. Significant history or presence of drug or alcohol misuse

6. Current use of any drugs taken through the nasal or inhaled route

7. Psychiatric illness including participants with a history of depression and/or
anxiety with associated severe psychiatric comorbidities, for example psychosis.

Consider exclusion in the following cases: (a) Participants with history of
anxiety-related symptoms of any severity within the last 2 years if the Generalized
Anxiety Disorder-7 score is ≥4; (b)Participants with a history of depression of any
severity within the last 2 years if the Patient Health Questionnaire-9 score is ≥4.
(c) severe claustrophobia

8. Current active smokers: equivalent to >5 cigarettes per week, including use of
tobacco in any form (e.g., smoking or chewing) or other nicotine-containing products
in any form (e.g., gum, patch) or electronic cigarettes.

Ex-smokers: Participants who have smoked >5 pack years at any time [5 pack years is
equivalent to one pack of 20 cigarettes a day for 5 years]. Ex-smokers that have
smoked <5 pack years at any time must not have smoked in the last 3 months.

9. Family history of 1st degree relative aged 50 years or less with sudden cardiac or
unexplained death

10. Personal or Family History of unexpectedly severe COVID-19 (including a personal
history of COVID-19 pneumonia), severe adverse response to any other viral disease
e.g., Guillain-Barré, or a family history (described as a 1st degree relative) with
clotting disorders

11. A total body weight of ≤ 45kg and a Body Mass Index (BMI) ≤18 kg/m2 and ≥28 kg/m2.
The upper limit of BMI may be increased to 30kg/m2 at the PI's discretion, in the
case of physically fit muscular individual

12. Venous access deemed inadequate for the phlebotomy demands of the study.

13. Any clinically significant abnormal finding on screening biochemistry, haematology
and microbiology blood tests or urinalysis apart from minor deviations which are
clinically acceptable and approved by the investigator.

Any of the following:

- Elevated HbA1C

- Positive HIV, active/chronic hepatitis B or C test.

14. A forced expiratory volume in 1 second (FEV1) and a forced vital capacity (FVC) <80%
of predicted value calculated using ATS/ERS guidance

15. Twelve-lead ECG recording with clinically relevant abnormalities as judged by the
study investigator.

16. History of, or currently active symptoms suggestive of upper or lower respiratory
tract infection (including reduced sense of taste and smell, raised body temperature
and/or persistent cough) within 4 weeks prior to viral challenge.

17. Presence of cold-like symptoms and/or fever (defined as participant presenting with
a temperature reading of >37.9ºC) on Day -1 and/or pre-challenge on Day 0.

18. Evidence of any respiratory virus infection (on Respiratory PCR from upper
respiratory tract sample) on admission to the quarantine unit, prior to challenge
virus inoculation.

19. Receipt of a live vaccine within 60 days prior to the planned date of viral
challenge, a non-live vaccine within 30 days prior to the planned date of viral
challenge or intention to receive any vaccination(s) before the day 28 follow-up
visit.

20. Receipt of blood or blood products, or loss (including blood donations) of 550 mL or
more of blood during the 3 months prior to the planned date of viral challenge or
planned during the 3 months after the final visit.

21. Medications:

1. Use of any medication or product (prescription or over the counter), for
symptoms of allergic rhinitis, nasal congestion or respiratory tract infections
or dermatitis/eczema including the use of regular nasal or medium-high potency
dermal corticosteroids, and antibiotics within 7 days prior to the planned date
of viral challenge apart from those described in Table 7, Permitted Medication
or agreed by the investigator

2. Receipt of any investigational drug within 3 months prior to the planned date
of viral challenge

3. Receipt of systemic (intravenous and/or oral) glucocorticoids or systemic
antiviral drugs within 6 months prior to the planned date of viral challenge.

4. Over the counter medications (e.g., paracetamol or ibuprofen) where the dose
taken over the preceding 7 days prior to the planned date of viral challenge
had exceeded the maximum permissible 24-hour dose (e.g., >4g per day of
paracetamol over the preceding week).

5. Chronically used medications, including any medication known to be a
moderate/potent inducer or inhibitor of cytochrome P450 enzymes, within 21 days
prior to the planned date of viral challenge.

6. Participants who have received any systemic chemotherapy agent,
immunoglobulins, or other cytotoxic or immunosuppressive drugs at any time.

22. Previous participation in a SARS-CoV-2 vaccine trial of a currently
unapproved/unlicensed vaccine in Singapore

23. Participant is mentally or legally incapacitated in the opinion of the Investigator.

24. Females who:

1. Are breastfeeding within 6 months of study commencement, or

2. Had been pregnant within 6 months prior to the study, or

3. Had a positive pregnancy test at any point during screening or prior to
inoculation with challenge virus

25. Anyone who is first degree related to anyone who is a delegated member of the
research team.

26. Any other reason that the Investigator considered made the participant unsuitable to
participate.

27. Participants with no knowledge of their family history.