Open Label Extension Study to Assess the Safety and Long-Term Immunogenicity of ARCT-021

A Phase 2a, Open Label Extension Study to Assess the Safety and Long-Term Immunogenicity of ARCT-021

This is an open-label study enrolling healthy adults that participated in Study ARCT-021-01 (the Parent Study). Participants will receive either a single injection of ARCT-021 or no injection and be followed for up to 365 days.

This is a phase 2a, open-label study enrolling up to 106 healthy adults that participated in Study ARCT-021-01 (the Parent Study). Participants will enter this study approximately 3 months after their final study visit in the Parent Study. Participants that received placebo in the Parent Study or who are seronegative for SARS-CoV-2 neutralizing antibodies at screening will receive a single dose of ARCT-021 and will be followed for 365 days. Participants that received two injections of ARCT-021 in the Parent Study will not receive any further injections of ARCT-021 and will be followed for 281 days.

Inclusion Criteria:

Individuals who:

1. are able to give consent

2. must have completed Study ARCT-021-01

3. agree to comply with all study visits and procedures

   Only for subjects that will receive ARCT-021 in this study:

4. are healthy and medically stable

5. are not planning to donate blood or plasma until 28 days after the last dose of ARCT-021.

6. are willing to refrain from strenuous exercise/activity and alcohol for at least 72 hours prior to study visits and until 28 days after the last dose of ARCT-021.

7. are willing to adhere to contraception requirements if sexually active and/or are of child-bearing potential

Exclusion Criteria:

Individuals who:

1. are unable to comply with the study visits or procedures in Study ARCT-021-01

2. received placebo in the Parent Study and who are not willing to receive ARCT-021 in this study.

   Only for subjects that will receive ARCT-021 in this study:

3. have or will receive any of the SARS CoV-2 or another experimental coronavirus during this study.

4. have a diagnosis of new clinically significant abnormalities including but not limited to

   • Respiratory disease requiring daily medications or oxygen currently or any treatment of respiratory disease exacerbations
   • Significant heart conditions
   • Significant neurological conditions
   • Significant blood disorders
   • Newly diagnosed autoimmune disease
   • Major surgery

5. have abnormal screening laboratory results

6. have uncontrolled diabetes

7. use of any prescription or over-the-counter medications within 7 days prior to vaccination

8. have received immunoglobulins and/or any blood or blood products

9. have a bleeding disorder

10. have uncontrolled blood pressure

11. have been treated with another investigational drug, biological agent, or device since completion of the Parent Study

12. have received or plan to receive:

    • A licensed, live vaccine within 4 weeks before or after study vaccination, or
    • A licensed, inactivated vaccine within 2 weeks before or after study vaccination

13. have traveled outside of Singapore within 30 days before the vaccination or plans to travel outside of Singapore within 60 days after vaccination.

14. other restrictions may apply