Please assess the completion status of the following clinical trial:

Trial Title: A Study to Evaluate Efficacy, Safety, and Immunogenicity of mRNA-1273 Vaccine in Adults Aged 18 Years and Older to Prevent COVID-19

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: PARALLEL
- Observational Model: None
- Primary Purpose: PREVENTION
- Time Perspective: None
- Masking: QUADRUPLE
- Phase: PHASE3
- Number of Arms: 2.0

Eligibility Criteria:
Inclusion Criteria:~* (Part A only) Participants who are at high risk of SARS-CoV-2 infection, defined as adults whose locations or circumstances put them at appreciable risk of exposure to SARS-CoV-2 and COVID-19.~* Understands and agrees to comply with the study procedures and provides written informed consent.~* Able to comply with study procedures based on the assessment of the Investigator.~* Female participants of non-childbearing potential may be enrolled in the study. Non-childbearing potential is defined as surgically sterile (history of bilateral tubal ligation, bilateral oophorectomy, hysterectomy) or postmenopausal (defined as amenorrhea for ≥12 consecutive months prior to Screening without an alternative medical cause). A follicle-stimulating hormone (FSH) level may be measured at the discretion of the Investigator to confirm postmenopausal status.~* Female participants of childbearing potential may be enrolled in the study if the participant fulfills all the following criteria:~  * Has a negative pregnancy test at Screening and on the day of the first dose (Day 1, open-label Day 1, and booster dose Day 1).~ * Has practiced adequate contraception or has abstained from all activities that could result in pregnancy for at least 28 days prior to the first dose (Day 1).~ * Has agreed to continue adequate contraception through 3 months following the last dose (Day 29, open-label Day 29, and booster dose Day 1).~ * Is not currently breastfeeding.~* 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 during the 3 months before enrollment.~* (Part C Only) Is currently enrolled in Part B of the current study (mRNA-1273-P301).~* (Part C Only) Has received at least 1 dose of mRNA-1273 in the current study (mRNA-1273-P301).~Exclusion Criteria:~* Is acutely ill or febrile 72 hours prior to or at Screening or dosing (Part B and Part C). Fever is defined as a body temperature ≥38.0°Celsius/100.4°Fahrenheit. Participants meeting this criterion may be rescheduled within the relevant window periods. Afebrile participants with minor illnesses can be enrolled/dosed at the discretion of the Investigator.~* Is pregnant or breastfeeding.~* (Part A Only) Known history of SARS-CoV-2 infection.~* Prior (Part A) or concurrent (Part B and Part C) administration of non-study coronavirus (SARS-CoV, Middle East Respiratory Syndrome \[MERS\]-CoV) vaccine or current/planned simultaneous participation in another interventional study to prevent or treat COVID-19.~* (Part A Only) Demonstrated inability to comply with the study procedures.~* An immediate family member or household member of this study's personnel.~* Known or suspected allergy or history of anaphylaxis, urticaria, or other significant adverse reaction to the vaccine or its excipients.~* Bleeding disorder considered a contraindication to intramuscular injection or phlebotomy.~* Has received or plans to receive a vaccine within 28 days prior to the first dose (Day 1) or plans to receive a non-study vaccine within 28 days prior to or after any dose of investigational product (IP) (except for seasonal influenza vaccine).~* (Part A only) Has participated in an interventional clinical study within 28 days prior to the day of enrollment.~* Immunosuppressive or immunodeficient state, including human immunodeficiency virus (HIV) infection, asplenia, and recurrent severe infections.~* Has received systemic immunosuppressants or immune-modifying drugs for \>14 days in total within 6 months prior to IP dose administration (for corticosteroids ≥20 milligram (mg)/day of prednisone equivalent).~* Has received systemic immunoglobulins or blood products within 3 months prior to the day of IP dose administration.~* Has donated ≥450 milliliters (mL) of blood products within 28 days prior to IP dose administration.

- Gender: ALL
- Minimum Age: 18 Years
- Maximum Age: None
- Healthy Volunteers: t

Study Arms:
- mRNA-1273 (Type: EXPERIMENTAL): Part A (Blinded): Participants will receive 1 intramuscular (IM) injection of 100 microgram (μg) mRNA-1273 on Day 1 and on Day 29.~Part B (Open-label): Participants who receive mRNA-1273-matching placebo during Part A and choose to be unblinded by participating in Part B, will receive 1 IM injection of 100 μg mRNA-1273 on Day 1 and Day 29. Participants who are only able to receive 1 dose of mRNA-1273 due to administrative reasons, will receive 1 IM injection of 100 μg mRNA-1273 on Day 1, if the participant chooses.~Part C: Eligible participants in Part B who choose to receive booster dose of mRNA-1273, will receive 1 IM injection of 50 μg mRNA-1273 on Day 1.
- Placebo (Type: PLACEBO_COMPARATOR): Part A only: Participants will receive 1 IM injection of mRNA-1273-matching placebo on Day 1 and on Day 29, if the participant chooses.

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