The purpose of this study is to evaluate the post-vaccination immune status at different time points in subjects immunized against Ebola Virus Disease; to select an optimal regimen of product administration; and, to assess safety of medicinal product GamEvac-Combi - Combined Vector-Based Vaccine against Ebola Virus Disease, 0.5 ml+0.5 ml/dose, following the immunization with a half (0.25 ml+0.25 ml/dose) and full (0.5 ml+0.5 ml/dose) therapeutic doses.

This clinical trial is designed as an open study to evaluate the duration of immunity persistence following the administration of medicinal product GamEvac-Combi - Combined Vector-Based Vaccine against Ebola Virus Disease.

It is an observational study; no interventions are planned in the course of common clinical practices during the study period; investigated therapeutic agents or special methods of examination will not be used in the study, except the blood sampling procedure specified in this Protocol. Only those patients who have signed the information consent form for participation in the study and have been informed by physician on the objectives and methods of this project will be involved in the study.

The study consists of a single stage which is designed as a follow-up period to observe volunteers vaccinated in the course of evaluation of safety, reactogenic properties and immunogenicity of product GamEvac-Combi - Combined Vector-Based Vaccine against Ebola Virus Disease in the dosages of 0.25 ml and 0.5 ml, during the study under Protocol 01-COMBI-2015 in October-November 2015. Vaccination will not be made within the present study. Screening of volunteers is not required: the study will involve as many of the volunteers as possible (but not more than 60 subjects) who had been immunized earlier with GamEvac-Combi - Combined Vector-Based Vaccine against Ebola Virus Disease, provided that they have no medical contraindications for blood sampling.

Study Schedule Visit 1 (outpatient): the goal of this visit is to assess whether a patient meets the inclusion/exclusion criteria. All procedures should be carried out upon receipt of the informed consent form signed by patient. The visit will be held 12 months after the vaccination.

Visit 2 (outpatient): 18 months after the vaccination. Visit 3 (outpatient): 24 months after the vaccination. The duration of immunity persistence following product administration will be assessed in healthy volunteers based on the measurements of specific antibody titers.

• by ELISA method 12, 18 and 24 months after the vaccination vs. baseline values;
• in virus neutralization reaction 12 months after the vaccination vs. baseline values.

Inclusion Criteria:

• Males and females aged 18-56 who had been earlier vaccinated with medicinal product GamEvac-Combi in the dosages of 0.25 ml and 0.5 ml, during the study under Protocol 01-COMBI-2015 in October-November 2015.
• Written informed consent signed by patients prior to their involvement in the study

Exclusion Criteria:

• Absence of the earlier vaccination with medicinal product GamEvac-Combi in the dosages of 0.25 ml and 0.5 ml, during the study under Protocol 01-COMBI-2015 in October-November 2015.
• Presence of a concomitant illness which could preclude obtaining a venous blood sample or affect the study process: (critical patient's condition, seizures, agitated state, blood loss and shocks of different origin).

The study will enroll up to 60 healthy volunteers of both genders aged 18-55 inclusive who had been earlier immunized with medicinal product GamEvac-Combi in the dosages of 0.25 ml and 0.5 ml, during the study under Protocol 01-COMBI-2015 in October-November 2015.