Seasonal influenza infections have a significant global impact leading to increased health and economic burden. The efficacy of currently available seasonal influenza vaccines targeting polymorphic surface antigens has historically been suboptimal. Cellular immune responses against highly conserved Influenza A virus antigens, such as nucleoprotein (NP) and matrix protein-1 (M1), have previously been shown to be associated with protection from disease, whilst viral-vectored vaccines are an effective strategy to boost cell-mediated immunity. We have previously demonstrated that MVA encoding NP and M1 can induce potent and persistent T cell responses against influenza. In this Phase I study, we evaluated the safety and immunogenicity of MVA-NP+M1, which was newly manufactured on an immortalized cell line, in six healthy adult participants. The vaccine was well-tolerated with only mild to moderate adverse events that resolved spontaneously and were comparable to previous studies with the same vaccine manufactured in chick embryo fibroblasts. A significant increase in vaccine-specific T cell responses was detected seven days after immunization and was directed against both antigens in the vector insert. This small Phase I study supports progression of this vaccine to a Phase IIb study to assess immunogenicity and additional protective efficacy in older adults receiving licensed seasonal influenza vaccines.
Keywords: heterosubtypic vaccine; immunogenicity; influenza; safety; viral vectors.