RSV Vaccine Research Advances with Launch of Novel A-strain Challenge Agent

A breakthrough RSV challenge agent

In developing a novel RSV challenge, we are advancing in Europe’s efforts to accelerate clinical validation of RSV therapies and vaccines through Controlled Human Infection Models (CHIM). These models safely replicate/simulate natural infection in healthy volunteers, enabling high-quality, data-driven assessment of vaccine and therapeutic efficacy before large-scale studies begin.

Our fully-validated, GMP manufactured RSV-NICA challenge agent is derived from an A-strain isolated in 2015. Being more recent than strains commonly used, it closely reflects currently circulating RSV viruses and demonstrates enhanced ability to reproduce natural infection symptoms, an essential criterion for high-quality CHIM studies.

Early proof-of-concept achieved

To generate early proof-of-concept data, on October 22, 2025, 12 healthy participants were inoculated with the RSV A-strain challenge agent at the SGS Clinical Pharmacology Unit in Antwerp, Belgium. Strategically located in the heart of Europe, this state-of-the-art center of excellence features 110 beds, of which 46 beds under BSL-2 conditions, a fully equipped GMP production facility, and a dedicated BSL-2 laboratory space. The facilities enable timely sample processing and – ensures rapid data turnaround to support critical go/no-go decisions.

Participants remained in a controlled quarantine environment for 11 days post-inoculation, during which standardized daily assessments of solicited symptoms and nasal swabs for qPCR and viral culture were performed.

One participant was excluded from the analysis due to a confirmed Rhinovirus co-infection. Among the remaining participants, 9 developed clinically relevant symptoms and all 11 demonstrated RSV detection by qPCR confirmed by viral culture, resulting in a 100% attack rate for this proof-of-concept cohort.

This study empirically validates the current inoculation titer as suitable for use in a CHIM. Furthermore, the observed potency of the RSV-NICA agent indicates that dose titration may be feasible without compromising statistical power, enabling optimization for future challenge studies.

Jelle Klein, Medical Director, SGS said: “As a leading European partner in infectious disease and vaccine research, we are delighted to have fulfilled our ambition to accelerate the route to clinical validation of novel RSV therapies and vaccines, bridging preclinical insights to human data through the development of this RSV-A strain challenge agent, the first of its kind worldwide.

“There is an urgent need to ensure that vaccines and therapeutics remain effective, available and affordable for patients. Today’s announcement reinforces SGS’s position as a trusted partner, delivering high-quality, decision-enabling data for both pharmaceutical and biotech companies in their pursuit of effective RSV treatment and prevention.”

Next steps

We can now support partners in accelerating the path to market for promising RSV vaccines and therapeutics. With the addition of RSV, SGS now offers one of the most comprehensive CHIM portfolios in Europe, including influenza, rhinovirus, malaria and RSV, further strengthening its role as a trusted partner for early-phase vaccine and therapeutic development.