MSD Links Bovine Serum in Vaccines to Salmon Spine Deformities

An MSD Animal Health study published in the Journal of Fish Diseases has identified fetal bovine serum (FBS) in oil-adjuvanted vaccines as a key risk factor for cross-stitch vertebrae (CSV) spinal deformities and reduced growth in farmed Atlantic salmon. Announced on 1 November 2026, the findings reinforce the serum-free positioning of MSD’s recently launched AQUAVAC S7 heptavalent salmon vaccine and signal substantial implications for aquaculture vaccine formulation across the global salmon farming industry.

The study tested five oil-adjuvanted vaccine (OAV) formulations with or without inactivated salmonid alphavirus (SAV) antigen and/or FBS, with Atlantic salmon monitored for approximately 10 months in a sea cage across different smoltification and temperature regimes. Fish given FBS-containing vaccines showed CSV prevalence of up to 51.7% and gross spinal pathology of up to 39.2%, while fish given FBS-free vaccines, including those with the SAV antigen, had CSV prevalence of 0% to 1.0%. Fish with 10 or more consecutively affected vertebrae had significantly lower slaughter weights, directly linking CSV severity to reduced growth, economic losses and welfare concerns.

Lead author Ragnar Thorarinsson, senior research scientist at MSD Animal Health, and Stephanie Steeves, global lead for Aqua at MSD Animal Health, positioned the findings around safer vaccine design. MSD Animal Health’s recently launched AQUAVAC S7, a heptavalent (seven-component) vaccine for farmed Atlantic salmon manufactured without serum components, aligns directly with the study’s implications. The findings also support the broader development of serum-free vaccines against diseases such as Pancreas Disease using inactivated whole-virus components. For the global salmon farming industry, where Norway, Chile, Scotland and Canada remain the dominant production hubs, CSV reduction represents substantial potential improvement in slaughter yield, feed conversion ratios and overall welfare metrics. Serum-free formulation also reduces supply chain exposure to variable animal-derived raw materials and aligns with growing retailer and consumer scrutiny of animal welfare in farmed seafood.

The commercial signal is a maturing aquaculture vaccine category where serum-free formulations materially reduce spinal deformity risk and support farmed salmon growth and welfare economics. AQUAVAC S7 positions MSD within that formulation shift. Expect sustained aquaculture vaccine innovation and continued focus on serum-free formulations across the global farmed salmon industry through 2027.

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