Seasonal influenza has a significant annual global impact. Current influenza vaccines work by inducing strain-specific antibodies against the highly polymorphic surface proteins of the influenza virus and need to be redesigned every year, increasing their cost and limiting availability. There is a demand for a more efficacious vaccine, particularly in older adults in which the current vaccines show poor efficacy. The aim is to investigate a novel vaccine, MVA-NP+M1, which targets T cell responses to the nucleoprotein and matrix 1 core proteins of the influenza virus A, which are highly conserved, and therefore may provide long protection against a broad range of influenza strains. INVICTUS is a phase IIb study to determine the safety and efficacy of candidate INfluenza Vaccine MVA-NP+M1 in combination with licensed InaCTivated inflUenza vaccine in adultS aged 65 years and above is a randomised, participant-blinded, placebo-controlled, multi-centre phase IIb efficacy study planned for 2030 volunteers aged 65 and over, in primary care. The primary objective is to assess the efficacy of MVA-NP+M1 co-administered with licensed inactivated quadrivalent influenza vaccine in adults ≥65 years. Participants complete daily diaries to record solicited and unsolicited events in the first four weeks post vaccination, and influenza-like illness (ILI) symptoms and severity throughout the influenza season. We hypothesise an improvement in the primary outcome, a reduction in the average number of days spent with moderate or severe influenza-like illness during periods of influenza circulation, in the group administered with MVA-NP+M1, compared to those in the control group. Registration: ClinicalTrials.gov identifier NCT03300362. Protocol version: INVICTUS Protocol v3.0, 08 June06 2018.