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.