06 November 2026
A controlled experimental study published in the Journal of Fish Diseases identifies residual foetal bovine serum (FBS) in oil-adjuvanted vaccines (OAVs) as a major risk factor for spinal deformities in Atlantic salmon (Salmo salar), particularly a condition known as "cross-stitch vertebrae" and platyspondyly.
Cross-stitch vertebral pathology had previously been associated with inactivated salmonid alphavirus (SAV) antigens used in vaccines against pancreas disease (PD). To identify the underlying trigger, researchers evaluated five multivalent OAV formulations, with or without inactivated SAV antigen and FBS, under different smoltification and temperature regimes.
Fish immunized with FBS-containing formulations exhibited significantly higher prevalences of gross perivertebral pathology (35.5%–39.2%), radiologically confirmed cross-stitch vertebrae (39.2%–51.7%), and platyspondyly, irrespective of SAV antigen presence or environmental rearing conditions. In contrast, formulations free of FBS, including those containing inactivated SAV antigen, resulted in near-zero prevalences of cross-stitch pathology (0%–1.0%).
Furthermore, the severity of vertebral lesions was directly associated with reduced specific growth rates (SGR) and lower slaughter weights, particularly in fish with ten or more consecutive affected vertebrae.
These findings suggest that residual mammalian cell culture components, rather than the viral antigen itself, are the primary drivers of this vaccine-associated skeletal pathology. The authors conclude that residual FBS content is a critical vaccine safety and quality parameter that warrants stringent evaluation in the risk–benefit assessment and formulation of commercial aquaculture vaccines.
Given evidence that formulations containing foetal bovine serum (FBS) residues induce an alarming 35%–50% prevalence of severe cross-stitch vertebral deformities, how did industry and regulators attribute this pathology solely to the viral antigen for years, failing to identify cell culture remnants as the primary safety risk during vaccine quality and safety evaluations?
Thorarinsson et al. (2026). Effect of Foetal Bovine Serum in Oil-Adjuvanted Vaccines on Spinal Deformities and Growth in Atlantic Salmon (Salmo salar). Journal of Fish Diseases, e70318.