A phase 1/2a clinical trial to assess safety and immunogenicity of an adenoviral-vectored capsular group B meningococcal vaccine

Capsular group B meningococcus (MenB) remains an important cause of disease globally, and additional vaccines against MenB would aid in reducing the incidence of infection. Previous work has demonstrated that a MenB adenoviral-vectored vaccine, ChAdOx1 MenB.1, elicited high serum bactericidal responses in preclinical models after a single dose, supporting further clinical development of this vaccine. Here, we report the results of a trial designed to assess the safety and immunogenicity of ChAdOx1 MenB.1 in healthy adults aged 18 to 50. In this phase 1/2a, single-center trial, participants received one or two doses of ChAdOx1 MenB.1 at days 0 and 180. One dose of ChAdOx1 MenB.1 was also given at day 180 to some individuals primed with one dose of 4CMenB at day 0. Participants recorded their symptoms in an electronic diary after vaccination, and safety blood readouts were monitored. Serum bactericidal antibody (SBA) assays were performed against a panel of MenB target strains. ChAdOx1 MenB.1 was well tolerated with no safety concerns and elicited protective SBA titers against a MenB strain expressing a homologous factor H-binding protein (fHbp) variant in 100% of participants after two doses. However, cross-reactivity analysis indicated a low SBA response to strains expressing heterologous fHbp, suggesting that a multivalent vaccine may be needed. In sum, ChAdOx1 MenB.1 is immunogenic in humans, and addition of another fHbp variant or of another antigen in this platform could provide an approach to extend protection against endemic MenB disease.