The product designated FMD-BO-A1-API-100 is an inactivated bivalent veterinary antigen concentrate prepared from foot-and-mouth disease virus serotypes O and Asia-1. It is supplied as a sterile-filtered liquid antigen pool or as a lyophilised intermediate stabilised with trehalose dihydrate and mannitol. The API is intended for downstream preparation of finished veterinary dose forms, including injectable water-in-oil-water emulsions, aqueous gel preparations, and—after lyophilisation and particle engineering—powders, granules, premixes, capsules, and tablets for species-specific administration where regional licensing accepts these presentations. The product also supports reconstitution to solution for injectable routes. The antigen content is standardised by serotype-specific virus neutralisation and 146S sucrose density gradient quantitation; each serial is checked for absence of residual live virus by three blind passages in BHK-21 and IB-RS-2 cell cultures according to WOAH Terrestrial Manual 2023 Chapter 3.1.8 and Ph. Eur. 0063. The liquid model is stored at 2–8 °C; the lyophilised model is sealed under vacuum and stored at 2–8 °C. The Type O antigen pool derives from a field isolate with an r1 value ≥ 0.30 against contemporary O/ME-SA/PanAsia-2 lineage isolates by two-dimensional virus neutralisation, and the Asia-1 antigen pool is matched to the Asia-1/Shamir lineage. Manufacturer's antigenic match data should be reviewed for regional field isolates because strain drift can reduce the r1 value.

FMD-BO-A1-API-100 denotes a liquid antigen payload of 100 finished vaccine doses per bottle at a nominal cattle dose of 2.0 mL. FMD-BO-A1-API-L denotes the lyophilised form with residual moisture ≤ 3.0% w/w by Karl Fischer titration. Release of the liquid concentrate includes confirmation of sterility, endotoxin content, pH, osmolality, identity, and 146S antigen mass. The lyophilised intermediate additionally requires residual moisture testing and reconstitution time. No thiomersal or antibiotics are added during inactivation; the API is compatible with downstream preservative-free adjuvants and stabiliser systems.

Which Release Specifications Govern the Inactivated Bivalent Antigen Concentrate?

Sterility is evaluated by membrane filtration according to Ph. Eur. 2.6.1. Bacterial endotoxins are measured by limulus amoebocyte lysate assay according to Ph. Eur. 2.6.14. Mycoplasma testing follows Ph. Eur. 2.6.7. Potency is not assigned to the API as a standalone unit; it is established on the finished vaccine in cattle via the 50% protective dose assay described in Chapter 3.1.8 of the WOAH Terrestrial Manual.

For downstream preparation of injectable water-in-oil-water double emulsions, the liquid API is diluted to a target antigen payload of 5–20 µg 146S per cattle dose of 2.0 mL. Primary emulsification under a high-shear rotor-stator mixer at 6,000–12,000 rpm uses light mineral oil and an emulsifier system with HLB 4.0–6.0; the secondary emulsification into an aqueous phase containing 1.0–2.0% w/v polysorbate 80 yields a double emulsion with dispersed aqueous droplets of 0.5–2.0 µm volume mean diameter when measured by laser diffraction. Finished emulsion viscosity ranges from 45 mPa·s to 90 mPa·s at 20 °C; higher values require widening the homogeniser gap to prevent temperature excursions above 30 °C. Aluminium hydroxide gel and saponin adjuvants are also suitable, but the total adjuvant solids must not exceed 2.0 mg/mL aluminium to prevent antigen precipitation and 146S loss during storage.

Inactivation Kinetics and Downstream Processing Boundaries

Virus harvests are inactivated with binary ethylenimine at 3–5 mM, 26 °C, 24 h, in a 1,500 L stirred-tank bioreactor equipped with pitched-blade impellers. First-order reduction rates of 0.12–0.18 log10 TCID50/h are recorded during validation; the acceptance criterion requires a total reduction of at least 6.0 log10 beyond the intercept, followed by sodium thiosulfate neutralisation at 20 mM. Process deviations at scale include pH drift below 7.0 in inadequately buffered harvests, which accelerates binary ethylenimine hydrolysis and produces tailing, and high residual cell debris that reduces 0.45 µm depth-filter capacity to approximately 150 L/m². Clarified antigen is concentrated by tangential-flow ultrafiltration through 100 kDa polyethersulfone cassettes; transmembrane pressure above 0.8 bar has been associated with 146S losses of 15–30% and visible aggregation. Diafiltration against 10 mM phosphate-buffered saline at pH 7.6 removes low-molecular-weight medium components; the retentate is then sterile-filtered through 0.22 µm polyvinylidene fluoride capsules. Mixing with stabilisers for lyophilisation is performed at 150 rpm for 15 min.

When solid-dose presentations are prepared, the stabilised liquid concentrate is lyophilised in stainless-steel trays at a fill depth of 8–12 mm. The freeze cycle ramps to -45 °C at 0.5 °C/min and holds for 4 h; primary drying at -20 °C and 50 µbar for 36 h yields a glassy cake. Milling through a 500 µm conical screen at 2,000 rpm yields a powder with span 1.5–2.5 by laser diffraction. Tablet compression at 10–15 kN on a rotary press fitted with 12 mm flat-fluted tooling produces cores with hardness 60–90 N and disintegration below 15 min by Ph. Eur. 2.9.1. Powder and granule blends for premixes are prepared by geometric dilution with lactose monohydrate at 2.0–5.0% w/w; capsule filling uses 400–600 mg fill weight in hard gelatin capsules. For reconstituted injectable solutions, the lyophilised intermediate is dissolved in sterile water for injection to a final volume of 100 mL. Published potency data for oral FMD antigen delivery in cattle remain limited; therefore, each regional dossier must include target-species immunogenicity studies rather than relying solely on parenteral PD₅₀ values.

When Potency Testing Follows WOAH Terrestrial Manual Chapter 3.1.8, What Acceptance Ranges Apply?

The bivalent finished vaccine is evaluated in cattle by the PD₅₀ method. For routine release, a dose must provide at least 3 PD₅₀ for each serotype unless the manufacturer's registered target is higher. Challenge strains are selected from homologous or antigenically matched field isolates; r1 values derived from virus neutralisation must be ≥ 0.30 for a strain to be considered a suitable match. In practice, the Type O component and Asia-1 component are individually adjusted to contribute 5–20 µg 146S per dose; reduction of one serotype below 5 µg may compromise cross-protection and increase the risk of subpotent lots. The bivalent format requires absence of immunological interference between the two components; batch-to-batch consistency is monitored by standardised challenge in vaccinated cattle and by antigenic mass assays. Published data for the specific Type O plus Asia-1 combination may be limited when field strains differ from the master seed; regional matching is therefore required.

The Product Differs from Monovalent and Trivalent Antigen Systems in the Following Operational Parameters

Compared with monovalent Type O or Asia-1 APIs, the bivalent product provides simultaneous coverage of two serotypes without the formulation burden of a third antigen. Compared with trivalent O/A/Asia-1 APIs, it reduces total antigen mass and may allow a more favourable liquid viscosity for injectable emulsions; however, it does not cover serotype A outbreaks. Compared with ready-to-use oil-emulsion finished vaccines, the API format permits manufacturer-specific adjuvant selection and solid-dose downstream processing. Compared with live attenuated or vector-derived vaccines, the inactivated whole-virus API carries no replication-competent pathogen; its primary limitation is dependence on parenteral adjuvantation for established potency. The following matrix summarises these differences.

Incompatibilities include cationic surfactants and high-concentration aluminium hydroxide above 2.0 mg/mL, which may precipitate the 146S particle; freezing of the liquid API below -5 °C without cryoprotectant causes aggregation. Use within 12 h after first opening of the liquid concentrate is required. For the lyophilised intermediate, exposure to ambient relative humidity above 60% before reconstitution may raise residual moisture above 3.0% w/w and reduce stability. Primary packaging is Type I glass vials with chloro-butyl stoppers; the liquid fill volume is 100 mL per vial.