Idorsia Ltd has announced additional positive clinical results for IDOR-1134-2831, its vaccine targeting Clostridioides difficile (C. difficile) in a phase 1 clinical pharmacology trial.
The glycan target of this vaccine is present on both bacteria and spores – the transmissible form of the pathogen responsible for spreading infection – of the most clinically relevant C. difficile strains, including hypervirulent variants. Following initial results in June 2025, which provided the first clinical validation for Idorsia’s synthetic glycan vaccine technology, the company advanced the program with a higher-dose cohort.
Results from healthy participants receiving the high dose confirmed that the vaccine is safe and well-tolerated. The vaccine induced a dose-dependent IgG response, with all participants receiving the high dose showing immunogenicity.
In further exploratory tests, the dose-dependent response was particularly pronounced for IgG1, a subclass known to play a key role in opsonisation, marking the pathogen for rapid identification and destruction by the immune system.
Idorsia’s vaccine is intended to be developed for the prevention of C. difficile infection (CDI) in patients at risk in both hospital and community settings, with the aim of providing broad protection against circulating strains.
Martine Clozel, chief scientific officer and head of research at Idorsia, said: “These new results from the high-dose cohort mark an important step forward for our synthetic glycan vaccine platform and reinforce our conviction that we are pioneering a fundamentally new approach to vaccination. The dose-dependent responses against the glycan target present on both C. difficile bacteria and spores, underscore the potential of this vaccine to go beyond traditional strategies and target the full life cycle of the pathogen.
“Beyond C. difficile, this technology has the potential to transform the landscape of vaccines, allowing prophylaxis against multiple bacteria and more. The fact that the antigens are synthesised in a chemistry laboratory offers immense opportunity. To fully realize this potential and accelerate development, we intend to advance this program in partnership.”
C. difficile is a spore-forming and toxin-producing bacterium. It is the leading cause of antibiotic-associated diarrhoea in developed countries. It infects the gastrointestinal tract, often following disruption of the gut microbiota, for example due to antibiotic use. CDI symptoms can range from mild diarrhoea to pseudomembranous colitis, which in some cases – particularly in the elderly – can lead to death. CDI is a major public health threat, particularly because recurrences are frequent, and is increasing with the aging population.
In the US, C. difficile is estimated to cause almost 400,000 infections each year. One in 11 people over 65 diagnosed with healthcare-associated CDI die within one month. C. difficile infections cause more than 25,000 deaths each year in the US alone. CDI places a significant economic burden on the healthcare system. The acute care direct costs of CDI are estimated to be $5-6bn per year in the US and €3bn per year in Europe.
Standard treatments of CDI are efficacious in clearing primary CDI. However, CDI recurs in up to 25% of treated patients. The C. difficile vaccine identified by Idorsia targets both spores and vegetative C. difficile bacteria and, therefore, could prevent not only colonisation but also transmission. Frail patients, elderly persons, persons in nursing homes, receiving antibiotic treatment, who are hospitalized, or expected to be hospitalised, represent target populations for this prophylactic vaccine.
Pathogenic bacteria like C. difficile express carbohydrates (glycans) on their surface which are recognized by the host’s immune system, leading to the production of glycan-specific antibodies. This makes glycans on the surface of pathogens attractive candidates for vaccine development.
The synthetic glycan in Idorsia’s C. difficile vaccine is synthesised in a carefully designed chemical process. This transforms a complex biochemical extraction, which is associated with heavy investment, into a purely chemical process driven by medicinal chemistry.
Idorsia’s C. difficile synthetic glycan vaccine has the advantage of being stable, immunogenic, fully characterisable, and the process has the potential to enable scalable and cost-efficient manufacturing.