Modelled evaluation of multi-component meningococcal vaccine (Bexsero®) for the prevention of invasive meningococcal disease in infants and adolescents in the UK.

Neisseria meningitidis is the main cause of bacterial meningitis and sepsis in the UK, and can potentially be lethal or cause long-term sequelae. Bexsero® (4CMenB) is a new multi-component vaccine approved by the European Commission for use in individuals aged ⩾2 months. A theoretical transmission model was constructed to assess the long-term effectiveness of Bexsero compared to standard care. The model was populated with UK-specific demographic data and calibrated to ensure that the transmission dynamics of meningococcal disease in the UK were adequately simulated. The model showed the best strategy to be a routine vaccination programme at ages 2, 3, 4, 12 months and 14 years combined with a 5-year catch-up programme in toddlers aged 12-24 months and adolescents aged 15-18 years. This would lead to a 94% reduction in meningococcal cases or 150 000 cases and 15 000 deaths over a 100-year time-frame.

A phase 2, randomized, blinded, dose-finding, controlled clinical trial to evaluate the safety, tolerability, and immunogenicity of a 24-valent pneumococcal conjugate vaccine (VAX-24) in healthy adults 65 years and older.

Despite current polysaccharide and conjugate vaccine use, pneumococcal diseases remain prevalent in older adults. VAX-24 is a 24-valent pneumococcal conjugate vaccine (PCV) containing eCRM, a proprietary carrier protein with non-native amino acids (para-azidomethyl-L-phenylalanine) that undergo site-specific conjugation to pneumococcal polysaccharides that have been activated with a small-molecule linker (dibenzocyclooctyne). Site-specific conjugation utilizing click chemistry enables consistent exposure of T-cell epitopes, reduction in carrier protein to pneumococcal polysaccharide ratio, and enhances manufacturing process consistency to improve PCVs by increasing serotype coverage while minimizing carrier suppression. Healthy adults aged 65 or older were randomized in a 1:1:1:1 ratio to receive a single injection of VAX-24 at 1 of 3 dose levels (1.1, 2.2, or a mixed dose of 2.2 or 4.4 mcg) or Prevnar 20® (PCV20) in a phase 2, blinded study. Primary outcome measures were solicited local and systemic events within 7 days post-vaccination, unsolicited adverse events (AEs) within 1 month, and serious AEs, medically attended AEs, or new onset of chronic disease within 6 months of vaccination. Serotype-specific opsonophagocytic activity (OPA) and immunoglobulin G (IgG) were measured pre-vaccination and at 1 month post-vaccination. Of 207 participants enrolled, 200 completed the trial. Safety profiles were comparable across the three VAX-24 doses and PCV20. Robust OPA and IgG immune responses were seen for all 24 serotypes. On average, immune responses to VAX-24 2.2 mcg dose were similar or higher compared to PCV20. In adults ≥ 65 years, VAX-24 had a safety profile similar to PCV20 through six months post-vaccination and induced robust OPA and IgG responses to all 24 serotypes, supporting prior data showing that site-specific conjugation allows for increased serotype coverage with similar or higher immune response vs other PCVs. The outcome of this phase 2 study further supports use of VAX-24 2.2 mcg dose in phase 3 trials. Clinicaltrials.gov: NCT05297578.

Serum bactericidal antibody assays - The role of complement in infection and immunity.

Complement is an essential component of the immune system and human pathogenic organisms have developed various mechanisms for evading complement mediated serum killing. The "gold standard" for measuring the ability of vaccine-induced antibody to kill Neisseria meningitidis is the serum bactericidal antibody (SBA) assay which measures complement mediated killing via antibody. This assay requires active complement, either intrinsic from the serum being tested or the addition of exogenous complement, either from a human or from another species such as rabbit. For serogroup C, an SBA titre of ≥4 was established as the correlate of protection when using human complement and ≥8 as the threshold when using rabbit complement, based on comparative assay results. Licensure of meningococcal vaccines, including polysaccharide protein conjugate vaccines and serogroup B vaccines has been based on the immune responses measured with the SBA assay, thus on a surrogate of vaccine efficacy. This review examines the use of complement and the SBA assay to assess immunity to meningococcal infection, and provides examples of vaccine trials in different age groups where various assays have been used.