The purpose of this study is to assess the immunogenicity and safety of MVC-COV1901 vaccine compared to AZD1222 in heathy adults.

The primary objective of the study is to measure the anti-SARS-CoV-2 neutralizing antibody titers in adult participants so as to demonstrate immunogenic superiority of MVC-COV1901 to the active control, AZD1222 vaccine, in terms of the GMT ratio of neutralizing antibodies at 14 days after the second dose of study intervention. This study also assesses the safety and tolerability of the study intervention and explores the immunogenicity in terms of anti-S IgG as well as the potential efficacy of MVC-COV1901 in preventing COVID-19.

Inclusion Criteria:

1. Male or female participant aged 18 years and above at randomization.

2. Healthy adults or adults with pre-existing medical conditions who are in stable condition. A stable medical condition is defined as disease not requiring significant change in therapy or hospitalization for worsening disease 3 months before enrollment and expected to remain stable for the duration of the study.

3. Female participants:

   1. A female participant is eligible is the participant is a woman of non-childbearing potential, ie, surgically sterilized or one year post-menopausal.
   2. If the participant is a woman of childbearing potential, she must agree to practice sexual abstinence or agree to use medically effective contraception from 14 days before screening to 30 days following the last administration of study intervention.
   3. Have a negative pregnancy test

4. Participant is willing and able to comply with all required study visits and follow-up required by this protocol.

5. Participant or the participant's legal representative must understand the procedures of the study and provide written informed consent.

Exclusion Criteria:

1. Pregnant or breast feeding or have plan to become pregnant within 30 days after the last administration of study intervention.
2. Employees at the investigator's site, of the Sponsor or delegate who are directly involved in the conduct of the study.
3. Currently receiving or received any investigational intervention within 30 days prior to the first dose of study intervention.
4. Administered any licensed live-attenuated vaccines within 28 days or other licensed non-live-attenuated vaccines within 7 days prior to the first dose of study intervention.
5. Administered any blood product or intravenous immunoglobulin administration within 12 weeks prior to the first dose of study intervention.
6. Currently receiving or anticipate to receive concomitant immunosuppressive or immune-modifying therapy within 12 weeks prior to the first dose of study intervention.
7. Currently receiving or anticipate to receive treatment with tumor necrosis factor (TNF)-α inhibitors within 12 weeks prior to the first dose of study intervention.
8. Major surgery or any radiation therapy within 12 weeks prior to the first dose of study intervention.
9. Has received any other investigational or approved COVID-19 vaccine.
10. Immunosuppressive illness or immunodeficient state.
11. A history of malignancy with potential risk for recurrence after curative treatment, or current diagnosis of or treatment for cancer.
12. Bleeding disorder considered a contraindication to IM injection or phlebotomy.
13. Known SARS-CoV-2 infection in the 3 months prior to the first dose of study intervention.
14. A history of cerebral venous sinus thrombosis, heparin-induced thrombocytopenia or antiphospholipid syndrome.
15. Participant who, in the investigator's judgement, is not in a stable condition and by participating in the study could adversely affect the safety of the participant, interfere with adherence to study requirements or evaluation of any study endpoint.
16. A history of hypersensitivity to any vaccine or a history of allergic disease or reactions likely to be exacerbated by any component of the MVC-COV1901 or AZD1222.
17. Body (oral, rectal, or ear) temperature ≥ 38.0°C or acute illness within 2 days before the first dose of study intervention.