Evaluating the Long Term Immunogenicity of Ebola Virus Vaccines Ad26-ZEBOV, MVA-BN-Filo and rVSV-ZEBOV

The Ebola Virus Disease (EVD), is caused by the viruses belonging to the genus Ebola virus. The disease occurs in sporadic outbreaks in the endemic zones of Africa and results in high mortality. During an outbreak, human to human to transmission occurs by contact with the body fluids of an infected individual. In the inter-endemic period the disease is zoonotically sustained in the environment. Prevention or control of future endemic outbreaks in the high risk areas of Africa will require effective preventative strategies including immunisation.

Cohort 1:

The Phase 1 study with the multiple heterologous prime boost regimes of the Ad26-ZEBOV and the MVA-BN-Filo vaccines demonstrated a substantive immunogenicity and safety of the vaccines. A combined immune response of humoral and cellular immunity was observed in the study participants. Furthermore, persistence of the immune response was evident at one year following the primary vaccination. It is not known whether the immune response persists beyond this time point. The duration of the immunological response is important as it will inform the clinical utility of the vaccines and whether or not additional booster dosage will be required and if so, at what interval.

In this study we will invite the 56 participants from the Phase 1 study at two time points: 24 - 30 months and 36 - 48 months after receiving the primary vaccination. Following consenting and enrolment into the study, the participants will undergo a blood test. We will assess the humoral immunity by estimating the level of binding antibody to the Ebola virus envelope glycoprotein. Cellular immunity will be assessed by estimating the functional CD4+ and the CD8+ T cells secreting the pro-inflammatory cytokines. We will undertake this assessment by intracellular staining of the peripheral blood mononuclear cells (PBMC) and using flowcytometry technique to identify the positively stained cells. A second assessment of the cellular immunity will be carried out by an in-house ELISpot technique subject to availability of additional funding.

Cohort 2: