Since its first outbreak occurred in 1976, Zaire Ebola virus have been associated with 14 outbreaks reported up to 2014. The Zaire Ebola virus in 2014 causing the most serious outbreak was considered to be a new epidemic strain, with GP homology of the gene was only 97.6%, compared to the GP gene of the strain in 1976. This investigational Ad5-EBOV vaccine was developed according to the 2014 epidemic Zaire strain and formulated as freeze-dry products which could be stored at 4℃.

In 2014, a single center, double-blind, placebo control, dose-escalation phase 1 clinical trial was performed in Taizhou, China. Our findings show that the Ad5-EBOV vaccine is safe and robustly immunogenic. One shot of the high dose vaccine could mount glycoprotein-specific humoral and T-cell response against Ebola virus in 14 days. The investigators intent to evaluate the safety and immunogenicity of a booster dose of the recombinant Ebola adenovirus vector vaccine (Ad5-EBOV) in healthy adults after primary immunization in this add in study. The investigators expect that the boosting immunization with a same vaccine for primary immunization is possible and could confer a longer-lived protection when needed.

The phase I trial has been unblind 28 days after the primary vaccination, but all the subjects are still kept blind as well as the laboratory staffs. Therefore, this booster vaccination trial will be conduct in single blind.

Inclusion Criteria:

• Participants who enrolled in the initial study, and completed the primary vaccination.
• Able to understand the content of the additional informed consent and willing to sign the additional informed consent for the boosting study
• Able and willing to complete a one-month follow-up.
• HIV negative
• Axillary temperature ≤37.0°C on the day of enrollment
• General good health as established by medical history and physical examination.

Exclusion Criteria:

New occurrence of any of the following situation after the primary vaccination:

• Subject that has a medical history of any of the following: allergic history of any vaccination or drugs, or allergic to any ingredient of the Ad5-EBOV vaccine, such as mannitol
• Woman who become pregnant after the primary vaccination or is positive in β-HCG (human chorionic gonadotropin) pregnancy test (urine) on day of enrollment for the boosting study
• Any acute fever disease or infections in last 7 days
• Not well-controlled chronic illness, such as asthma, diabetes, or thyroid disease
• Hereditary angioneurotic edema or acquired angioneurotic edema
• Urticaria in last 6 months
• Asplenia or functional asplenia
• Platelet disorder or other bleeding disorder may cause injection contraindication
• Faint at the sight of blood or 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
• Any condition that in the opinion of the investigators may interfere with the evaluation of study objectives