Please assess the completion status of the following clinical trial:

Trial Title: A Phase II Clinical Trial to Evaluate the Recombinant Vaccine for COVID-19 (Adenovirus Vector)

Study Design Characteristics:
- Allocation: RANDOMIZED
- Intervention Model: CROSSOVER
- Observational Model: None
- Primary Purpose: PREVENTION
- Time Perspective: None
- Masking: DOUBLE
- Phase: PHASE2
- Number of Arms: 3.0

Eligibility Criteria:
Inclusion Criteria:~* Aged between 18 and 60 years.~* Able to understand the content of informed consent and willing to sign the informed consent~* Able and willing to complete all the secluded study process during the whole 6 months study follow-up period.~* Negative in HIV diagnostic test.~* Negative in serum antibodies (IgG and IgM) screening of COVID-19.~* Axillary temperature ≤37.0°C.~* The BMI index is 18.5-30.0.~* General good health as established by medical history and physical examination.~Exclusion Criteria:~* Family history of seizure, epilepsy, brain or mental disease~* Subject allergic to any component of the investigational vaccine, or a more severe allergic reaction and history of allergies in the past.~* Woman who is pregnant, breast-feeding or positive in β-HCG (human chorionic gonadotropin) pregnancy test (urine) on day of enrollment, or become pregnant during the next 6 months~* Any acute fever disease or infections.~* History of SARS~* Major congenital defects or not well-controlled chronic illness, such as asthma, diabetes, or thyroid disease.~* Serious cardiovascular diseases, such as arrhythmia, conduction block, myocardial infarction, severe hypertension without controllable drugs, etc.~* Hereditary angioneurotic edema or acquired angioneurotic edema~* Urticaria in last one year~* No spleen or functional spleen.~* Platelet disorder or other bleeding disorder may cause injection contraindication~* Faint at the sight of needles.~* Prior administration of immunodepressant or corticosteroids, antianaphylaxis treatment, cytotoxic treatment in last 6 months.~* Prior administration of blood products in last 4 months~* Prior administration of other research medicines in last 1 month~* Prior administration of attenuated vaccine in last 1 month~* Prior administration of inactivated vaccine in last 14 days~* Current anti-tuberculosis prophylaxis or therapy~* According to the judgement of investigator,various medical, psychological, social or other conditions, those could affect the subjects to sign informed consent.

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

Study Arms:
- Arm 1 (Type: ACTIVE_COMPARATOR): 1×10\^11vp of Ad5-nCoV administered through 1.0 mL intramuscular injection in the deltoid muscle on Day 0
- Arm 2 (Type: ACTIVE_COMPARATOR): 5×10\^10vp of Ad5-nCoV administered through 1.0 mL intramuscular injection in the deltoid muscle on Day 0
- Arm 3 (Type: PLACEBO_COMPARATOR): Placebo administered through 1.0 mL intramuscular injection in the deltoid muscle on Day 0

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