Haemophilus parasuis Vaccine Veterinary Grade API for Tablets / Injections / Capsules / Powders / Granules / Premix / Solutions is manufactured as an inactivated whole-cell antigen concentrate derived from H. parasuis serovars 4 and 5. Two model designations are released: HP-VAC-API-LYO, a lyophilized powder intended for solid oral dosage forms, dry granules, and premix blends; and HP-VAC-API-LIQ, a chilled aqueous concentrate for injectable solutions, oral drenches, and liquid premixes. The freeze-dried cake is stabilized with trehalose and mannitol at a total cryoprotectant-to-antigen mass ratio of 3:1. Release specifications include sterility by Ph. Eur. 2.6.1, bacterial endotoxin less than 50 EU/mL, residual formaldehyde less than 0.02% v/v, residual moisture less than 3.0% w/w for the lyophilized presentation, and pH 7.0–7.6 after reconstitution. The concentrate is supplied without aluminium hydroxide, mineral oil, thiomersal, or animal-origin stabilizers; downstream manufacturers add adjuvants, preservatives, or enteric polymers after formulation development.

The material is classified as a veterinary vaccine active substance, not a finished vaccine. It is intended for incorporation into licensed or autogenous vaccine products by manufacturers operating under EU GMP Part II or equivalent national veterinary biological product standards. Use of the API in oral solid dosage forms requires enteric protection because porcine gastric secretion at pH 2.0–3.5 and pepsin activity degrade unprotected whole-cell antigen. No fixed target animal dose is assigned at the API stage; dose is derived from finished product potency after formulation and adjuvant selection.

What inactivation and purity specifications apply to this antigen concentrate?

The inactivation procedure uses formaldehyde at 0.05% v/v to 0.1% v/v for 18–24 h at 37°C, followed by neutralization with sodium metabisulfite at 0.5–1.0 g/L. Inactivation is confirmed by two consecutive blind passages on modified chocolate agar at 37°C for 72 h; no viable colonies are recovered. Identity is confirmed by slide agglutination with monospecific antisera against serovar 4 and serovar 5. Antigenic mass is standardized to a pre-inactivation cell density equivalent to 1×10^9–5×10^9 CFU/mL, and the final total protein in HP-VAC-API-LIQ is adjusted to 8–14 mg/mL. The lyophilized powder contains trehalose and mannitol as cryoprotectants; residual moisture is controlled below 3.0% w/w by Ph. Eur. 2.5.12. Bacterial endotoxin testing by Ph. Eur. 2.6.14 uses a limit of 50 EU/mL because whole-cell H. parasuis lipooligosaccharide is intrinsically pyrogenic at higher concentrations. Batch release also includes visual inspection for cake collapse, reconstitution time less than 120 s in sterile water at 20–25°C, and total aerobic microbial count below 10 CFU/g for the lyophilized powder before sterility is confirmed.

For tablets, capsules, powders, granules, and premix presentations, the lyophilized antigen powder is first blended with enteric protectants such as hydroxypropyl methylcellulose acetate succinate or methacrylic acid-ethyl acrylate copolymer at a coating polymer-to-antigen weight ratio of 1:1 to 3:1. Unprotected antigen exposed to porcine gastric pH below 3.0 and pepsin activity above 250 U/mL loses detectable seroreactivity within 30–45 min in simulated gastric fluid at 39°C. Fluid-bed granulation is therefore operated with inlet air temperature 40–45°C, product temperature below 30°C, and aqueous binder spray rate 10–20 g/min. Wet mass is dried to loss-on-drying below 4.0% w/w before tableting. Direct compression is restricted to excipient matrices with compression pressure below 80 MPa; at 100 MPa, antigen recovery in dissolution buffer falls below 70% in transfer studies using comparable lyophilized bacterial antigens. Capsule filling on dosator machines requires powder bed relative humidity below 30% RH to prevent sticking and dose variability above 5% RSD. Published data for this specific configuration is limited; the stated limits reflect transfer studies from comparable lyophilized bacterial antigen formulations rather than a public monographic specification.

Premix and granule manufacture on a ribbon blender with 500 kg capacity requires geometric dilution of the concentrated antigen powder into a carrier such as lactose monohydrate or dextrose monohydrate. Direct addition of the concentrated powder to the blender without pre-blending produces segregation at the blender ends and antigen recovery losses above 15% after 10 min at 25 rpm. Milled granulation fines below 45 µm increase dust and cross-contamination risk in non-dedicated facilities. The final premix is controlled to 1×10^8–1×10^9 CFU-equivalent/g and loss-on-drying below 4.0% w/w.

When the antigen is formulated for injectable solutions, adjuvant choice sets reactogenicity boundaries

Injectable formulations prepared from HP-VAC-API-LIQ require separate addition of adjuvant. Aluminium hydroxide gel at 0.5–2.0 mg Al³⁺/mL is compatible within pH 7.0–7.6 and produces a depot effect without exceeding the endotoxin release threshold of the finished vaccine. Adsorption efficiency above 90% should be confirmed by centrifugal depletion or enzyme-linked immunosorbent assay of the supernatant; incomplete adsorption below 85% alters the local reactogenicity profile. Oil-in-water adjuvants containing squalene or mineral oil increase local inflammation and should be evaluated for total antigen adsorption and droplet size distribution 1–10 µm by laser diffraction. Inline filtration through 0.45 µm membranes is not recommended for the liquid concentrate because whole-cell antigen aggregates above 10 µm may be retained; a 5 µm prefilter is used before final sterile filtration of adjuvanted emulsion formulations. Final dose volumes for pigs are typically 1.0–2.0 mL by intramuscular injection, although the API itself does not carry a fixed dose claim. Sterility of the finished injectable product is verified after adjuvant addition because the API release sterility does not cover downstream compounding.

Preservative compatibility is limited. Thiomersal and benzalkonium chloride at routine concentrations produce antigen precipitation when added to HP-VAC-API-LIQ at 2–8°C for more than 48 h. Formulation development should therefore use single-dose presentations or verify chemical inactivation of the preservative before antigen addition. The liquid concentrate should be equilibrated to 20–25°C before aseptic transfer to avoid cold precipitation of stabilizers.

Processing equipment constraints during lyophilized powder conversion

Lyophilization is conducted in a 20 m² shelf freeze-dryer with shelf ramp from −40°C to +30°C at 0.4°C/min and chamber pressure 0.15–0.25 mbar. Primary drying is held at −20°C for 18–24 h; secondary drying is held at +30°C for 6–8 h. The resulting cake is milled under nitrogen to D90 < 75 µm for capsule filling and dry granulation. Cake collapse is observed when shelf temperature exceeds −15°C before the residual moisture falls below 5.0% w/w, and collapsed lots show reconstitution times above 180 s. Milling temperatures are maintained below 25°C because antigen denaturation accelerates above 40°C in dry powder. Particle size distribution by laser diffraction is monitored at D10 15–25 µm, D50 35–50 µm, and D90 65–75 µm for consistent tablet compressibility and premix homogeneity. If the powder is intended for direct compression, fused silica or microcrystalline cellulose is added at 10–20% w/w to improve flow; angle of repose above 40° indicates poor flow and requires granulation.

The principal difference from ready-to-use H. parasuis bacterins is the absence of adjuvant and preservative in the API. Commercial monovalent and bivalent bacterins are commonly supplied with aluminium hydroxide or oil adjuvants and are licensed for parenteral administration only. This antigen concentrate can be formulated into enteric-coated oral dosage forms because the lyophilized powder is not adsorbed to adjuvant particles. Compared with recombinant subunit vaccines that express selected outer membrane proteins, the whole-cell API retains native H. parasuis outer membrane vesicles, lipooligosaccharide-associated epitopes, and surface proteins associated with serovar-specific agglutination. Consequently, residual endotoxin control is more critical than with subunit antigens, and the release limit of 50 EU/mL is lower than many crude bacterial extracts. The fixed serovar 4 and serovar 5 profile differs from autogenous products based on farm-specific isolates, but the API can be blended by a licensed manufacturer into an autogenous final product if local regulatory approval so permits. The product is not a sterile final vaccine and cannot be administered directly to animals without formulation and batch release by a competent manufacturer.

Unlike live attenuated H. parasuis candidates, the inactivated whole-cell antigen does not require cold-chain below −20°C and carries no risk of reversion or shedding in vaccinated herds. However, the immune response is primarily humoral with shorter duration than live vaccines in published challenge models; no cross-protection against heterologous serovars is guaranteed beyond the stated serovar profile. These limitations are critical for vaccination programs in multi-source nursery flows.

The antigen demonstrates dose-dependent stability in finished premix and solution matrices

Stability data generated under veterinary storage conditions indicate that the lyophilized powder retains relative potency above 90% for 24 months at 2–8°C. Reconstituted liquid concentrate is assigned a shelf life of 12 months at 2–8°C, with 30 days at 25°C as an accelerated excursion condition. In finished premix formulations containing organic acids, antigen recovery after 28 days at 25°C/60% RH falls below 80% if the matrix pH is below 4.5; coated granules buffered with calcium carbonate to pH 5.5–6.5 maintain greater than 85% recovery in the same period. These figures are product-specific stability acceptance criteria, not regulatory claims for final market authorization. Freeze-thaw stress in the liquid concentrate shows aggregation above 10 µm after 3 cycles from −20°C to room temperature. Photostability under 2000 lux visible light and 10 W/m² UV-A for 24 h shows a potency loss below 5% when stored in amber glass, but clear glass containers produce a loss above 15% in the same conditions.

The liquid concentrate should not be frozen; repeated freeze-thaw cycles greater than 3 produce insoluble aggregates that cannot be redispersed without high-shear mixing. The antigen is incompatible with oxidising agents, cationic polymers, and amine-based buffers above pH 8.0 because alkaline conditions accelerate hydrolysis of surface protein epitopes. Formaldehyde-releasing preservatives should not be added to the final formulation without considering the residual formaldehyde specification. The lyophilized powder should be handled at relative humidity below 30% RH to prevent moisture uptake and caking during weighing. Final dosage forms intended for oral administration require enteric protection; unprotected tablets or uncoated granules are not expected to survive gastric passage in pigs. The API should not be combined with live attenuated bacterial vaccines in the same diluent without compatibility testing because preservative-free antigen concentrates may support microbial growth after accidental contamination. These boundaries define the operational space for downstream formulation and should be verified in the receiving manufacturer’s equipment train.