World's First RSV B Human Challenge Model Shows High Infection Rates
hVIVO has developed the first RSV B human challenge model to support next-generation vaccines. The model achieved ~90% infection rates and strong symptomatic disease, outperforming the established RSV A model. Challenge trials are increasingly accepted by regulators to accelerate vaccine development.
The world’s first RSV B human challenge model has been developed, demonstrating high infection rates and strong symptomatic disease in an initial clinical study. The model, created by hVIVO, aims to support the development of next-generation vaccines targeting both RSV A and B strains, as well as hMPV.
Most first-generation RSV vaccines were tested only against RSV A challenge viruses, but the field is now advancing bivalent and trivalent candidates that include RSV B antigens. hVIVO’s new RSV B model was designed to fill this gap and provide a tool to evaluate these combination vaccines thoroughly.
To develop the challenge virus, the company collected clinical isolates from household contacts and hospitalized patients, screening candidates against a broad pathogen panel. A suitable isolate was then grown on GMP-compliant cell lines with minimal passage to avoid adaptation, followed by extensive safety testing including next-generation sequencing. The resulting GMP-manufactured virus closely reflects circulating strains.
In the first clinical evaluation, the RSV B model achieved an approximate 90% infection rate by PCR criteria and produced robust symptomatic disease, with high levels of moderate to severe symptoms. When compared with hVIVO’s established RSV A Memphis model, the B strain generated higher disease levels across all key endpoints, suggesting strong translational value for vaccine and antiviral testing.
Regulatory agencies have shown increasing receptivity to human challenge trial data. Several RSV vaccines have received expedited designations, such as Fast Track and Breakthrough status, based in part on challenge study results. These trials can help refine dose selection, identify appropriate endpoints, and provide early efficacy signals to accelerate development, though they remain a complement to, not a replacement for, large-scale field studies.