Consultation report - gonococcal immunoassays and standards for vaccine development

Gonorrhoea is a sexually transmitted infection with adverse outcomes for sexual, reproductive and neonatal health. Additionally, the bacterium, Neisseria gonorrhoeae, has demonstrated increasing resistance against multiple classes of antimicrobials, making combatting gonorrhoea a priority for the World Health Organization. An effective vaccine would have substantial global public health benefit and a major impact on the silent pandemic of antimicrobial resistance. Several candidate gonococcal vaccines, representing a number of vaccine platforms, are in pre-clinical development. In addition, a number of clinical studies are underway to assess the efficacy of the meningococcal group B vaccine, 4CMenB, against gonorrhoea. A major challenge in comparing gonococcal vaccine candidates and vaccine-induced immune responses is the lack of standardised and harmonised immunoassays. At present, immunogenicity of the different vaccine formulations is measured through assays which have been developed independently in different laboratories. As the development of candidate gonococcal vaccines moves into clinical trials, improved harmonisation in the measurement of immunogenicity is key for comparing vaccine responses across trials. This requires international standards, including an international serum standard for gonococcal immunoassays, and a panel of standard target strains, which are currently lacking. A further complication is the lack of knowledge about immune correlates of protection against gonorrhoea, and, therefore, the most appropriate assays to use to assess the immune response to a candidate vaccine. As further data are gathered from clinical studies exploring protection against gonorrhoea provided by 4CMenB, it may be possible to discern correlates of protection, but this also requires standardised assays. A workshop was held at Keble College, Oxford, United Kingdom in April 2024, with participation from vaccine developers, regulators and assay standardisation specialists. Its goal was to advance discussions on gonococcal immunoassay standardisation priorities, including generation of a gonococcal international reference serum. The meeting discussion, outcomes and recommendations are outlined in this report.