Strategic and scientific contributions of human challenge trials for vaccine development: facts versus fantasy

Reverse development of vaccines against antimicrobial-resistant pathogens

Vaccine R&D is typically a lengthy process taking >10 years. However, vaccines still fail in clinical development because of unreliable animal models or absent immunological correlates of protection. Without a correlate of protection, phase-1 and -2 studies of safety and immunogenicity can fail to predict phase-3 efficacy. Indeed, the history of vaccine development is replete with promising phase-1 and -2 results and failed phase-3 efficacy trials. To avoid this misfortune, we present Reverse Vaccine Development for vaccines against antimicrobial-resistant (AMR) pathogens. In this approach, instead of evaluating efficacy in phase 3, proof-of-principle efficacy is evaluated as early as possible in a population with a high incidence of disease, which may differ from the population intended for registration, and can be a controlled human infection population. To identify a correlate of protection in these populations, the vaccine-elicited immune response is compared between protected and unprotected subjects. If a correlate is identified, it can help to refine the vaccine dosage, schedule, and formulation, and facilitate the assessment of vaccine efficacy in other populations with different attack rates, subject characteristics, and disease manifestations. This may be the only way to provide life-saving vaccines to populations affected by AMR-pathogen diseases at incidences that are typically low and unsuited to phase-3 efficacy trials. The availability of a correlate of protection early in clinical development can potentially prevent failures of large phase-3 trials and unnecessary exposures of populations to inefficacious vaccines that have resulted in disinvestment in the development of vaccines against AMR pathogens.

Fourth Controlled Human Infection Model (CHIM) meeting, CHIM regulatory issues, May 24, 2023

Many aspects of Controlled Human Infection Models (CHIMs, also known as human challenge studies and human infection studies) have been discussed extensively, including Good Manufacturing Practice (GMP) production of the challenge agent, CHIM ethics, environmental safety in CHIM, recruitment, community engagement, advertising and incentives, pre-existing immunity, and clinical, immunological, and microbiological endpoints. The fourth CHIM meeting focused on regulation of CHIM studies, bringing together scientists and regulators from high-, middle-, and low-income countries, to discuss barriers and hurdles in CHIM regulation. Valuable initiatives for regulation of CHIMs have already been undertaken but further capacity building remains essential. The Wellcome Considerations document is a good starting point for further discussions.

Controlled human infection trials: Legitimacy and conditions of implementation in France

This round table is the result of an observation. The observation being that controlled human infection clinical trials (also called "infectious challenge" trials or "Controlled Human Infection Models", "CHIM") recommended or even encouraged in the context of vaccine developments in particular, are not carried out in France. However, there are no formal prohibitions within regulations or ethical principles, which point to the prior assessment of risks and benefits for individuals and for society. The participants in this Round Table thus wished to examine, through the prism of their respective disciplines, the scientific and medical relevance of conducting such trials in France and, if possible, to imagine the conditions under which they would be carried out, thus resulting in recommendations on (1) the advisability of their conduct in France (2), the conditions under which they would be implemented in terms of logistics and regulations, and (3) their social acceptability. The recommendations on which the participants of the Round Table came to an agreement are presented as the analysis progresses.

Novel Influenza Vaccines: From Research and Development (R&D) Challenges to Regulatory Responses

Influenza vaccines faced significant challenges in achieving sufficient protective efficacy and production efficiency in the past. In recent decades, novel influenza vaccines, characterized by efficient and scalable production, advanced platforms, and new adjuvant technologies, have overcome some of these weaknesses and have been widely licensed. Furthermore, researchers are actively pursuing the development of next-generation and universal influenza vaccines to provide comprehensive protection against potential pandemic subtypes or strains. However, new challenges have emerged as these novel vaccines undergo evaluation and authorization. In this review, we primarily outline the critical challenges and advancements in research and development (R&D) and highlight the improvements in regulatory responses for influenza vaccines.