Clinical challenges in vaccine and monoclonal antibody development against ESCAPE pathogens: insights from EMA...

Combating ESCAPE pathogens (E. faecium, S. aureus, C. difficile, A. baumannii, P. aeruginosa, and Enterobacteriaceae) remains a major public health concern due to their treatment resistance and immune evasion. Vaccines and monoclonal antibodies (mAbs) are promising solutions, yet only one mAb is licensed and no vaccine has reached that stage. To identify recurring clinical challenges, we analyzed final advice letters (FALs) issued through the European Medicines Agency's (EMA) Scientific Advice procedure.

We searched both the Paul-Ehrlich-Institut local database and the EMA database for FALs on vaccines and mAbs targeting ESCAPE pathogens. We included FALs that matched the pathogen and product criteria and addressed clinical development. We excluded those focused solely on quality, non-clinical, safety, or post-marketing aspects. From the included FALs, we extracted information across four main categories: primary endpoint, statistical analyses, study population, and study design. Regulatory responses were classified as fully, silently, partially, or not endorsed. We subsequently reviewed related clinical trial protocols to assess whether recommendations were implemented and to provide a narrative summary of changes to the development programs.

We included 14 FALs for each of the two medicine categories, related to six vaccine and 13 mAb trials. To address common challenges across the primary endpoints, regulators recommended selecting single, infection-related endpoints and emphasized precise clinical and laboratory case definitions to ensure attribution of infection to the target pathogen. They further advised on incorporating supportive evidence, such as subgroup analyses of cases or inflammation markers, direct microbiological or indirect measures (e.g., antibiotic use, hospital stay), or survival-related endpoints. Recommendations for study populations focused on refining the inclusion/exclusion criteria to identify those most likely to benefit. Regulators also advised on changes in the statistical analysis plan (mainly due to lower-than-expected incidence) and generally discouraged single pivotal trials.

The development of vaccines and mAbs against ESCAPE pathogens is challenged by pathogen diversity, unpredictable infection rates, heterogeneous trial populations, and diagnostic uncertainty. In a field with no one-size-fits-all development pathway, early regulatory interaction and multidisciplinary disease-expert input are essential to reduce uncertainty and support robust, efficient clinical development programs.