Please assess the completion status of the following clinical trial:

Trial Title: Efficacy of Different COVID-19 Vaccine Combinations in Inducing Long-term Humoral Immunity [PRIBIVAC]

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: PARALLEL
- Observational Model: None
- Primary Purpose: PREVENTION
- Time Perspective: None
- Masking: SINGLE
- Phase: PHASE4
- Number of Arms: 4.0

Eligibility Criteria:
Inclusion Criteria:~1. Willing and able to provide informed consent for participation in this study;~2. Aged ≥21years at the time of study enrolment;~3. Received the second dose of BNT162b2 or mRNA-1273 Coronavirus Disease 2019 vaccines at least 6 months prior to enrolment;~4. Willing and able to comply with all scheduled visits, vaccination plan, laboratory tests and other study procedures.~For Phase D inclusion criteria 3 will be amended to 'Received the first booster dose of BNT162b2 or mRNA-1273 Coronavirus Disease 2019 vaccine at least 5 months prior to enrolment'. Only individuals recommended to receive a second booster dose under MOH recommendations will be enrolled.~Exclusion Criteria:~1. Known history of SARS-CoV-2 or SARS-CoV-1 infection;~2. Previously received an investigational coronavirus vaccine;~3. Previously received a SARS-CoV-2 monoclonal antibody;~4. Current or planned simultaneous participation in another interventional study;~5. A history of anaphylaxis, urticaria, or other significant adverse reaction requiring medical intervention after receipt of a COVID-19 vaccine, or otherwise have a contraindication to one of the available study vaccines per the approved label;~6. Individuals who are immunocompromised (e.g. active leukaemia or lymphoma, generalised malignancy, aplastic anaemia, solid organ transplant, bone marrow transplant, current radiation therapy congenital immunodeficiency, HIV/AIDS with CD4 lymphocyte count \< 200 and patients on immunosuppressant medications);~7. Received systemic immunosuppressants or immune-modifying drugs for \>14 days in total within 6 months prior to Screening (for corticosteroids \>/= 20 milligram per day of prednisone equivalent). Topical tacrolimus is allowed if not used within 14 days prior to Day 1;~8. Individuals who are pregnant or breast feeding;~9. Chronic illness that, in the opinion of the study team, is at a stage where it might interfere with trial conduct or completion;~10. Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalised involuntarily;~11. Current alcohol abuse or drug addiction that might interfere with the ability to comply with trial procedures in the opinion of the study team;~12. Moderate or severe acute illness/infection (according to study team's judgement) on the day of vaccination, or febrile illness (temperature ≥ 37.5°C). A prospective participant should not be included in the study until the condition has resolved or the febrile event has subsided.~For Phase D of the trial exclusion criteria 1 and 4 will no longer apply: exclusion criteria 1 is no longer relevant as it not a consideration in MOH recommendations for COVID-19 booster vaccination, and exclusion criteria 4 because of the broad recommendations from MOH for keeping up to date with COVID-19 boosters.

- Gender: ALL
- Minimum Age: 21 Years
- Maximum Age: None
- Healthy Volunteers: t

Study Arms:
- Homologous mRNA booster vaccine (Type: ACTIVE_COMPARATOR): BNT162b2 + BNT162b2 + BNT162b2 or mRNA-1273 + mRNA-1273 + mRNA-1273
- Heterologous mRNA booster vaccine (Type: EXPERIMENTAL): BNT162b2 + BNT162b2 + mRNA-1273 or mRNA-1273 + mRNA-1273 + BNT162b2
- COVAXIN (Type: EXPERIMENTAL): BNT162b2 + BNT162b2 + COVAXIN or mRNA-1273 + mRNA-1273 + COVAXIN
- Nuvaxovid (Type: EXPERIMENTAL): BNT162b2 + BNT162b2 + Nuvaxovid or mRNA-1273 + mRNA-1273 + Nuvaxovid

Based on this trial design, predict the completion outcome and termination type (if applicable).