Suitability of differently formulated dry powder Newcastle disease vaccines for mass vaccination of poultry.

Dry powders containing a live-attenuated Newcastle disease vaccine (LZ58 strain) and intended for mass vaccination of poultry were prepared by spray drying using mannitol in combination with trehalose or inositol, polyvinylpyrrolidone (PVP) and/or bovine serum albumin (BSA) as stabilizers. These powders were evaluated for vaccine stabilizing capacity during production and storage (at 6 °C and 25 °C), moisture content, hygroscopicity and dry powder dispersibility. A mixture design, varying the ratio of mannitol, inositol and BSA, was used to select the stabilizer combination which resulted in the desired powder properties (i.e. good vaccine stability during production and storage, low moisture content and hygroscopicity and good dry dispersibility). Inositol-containing powders had the same vaccine stabilizing capacity as trehalose powders, but were less hygroscopic. Incorporation of BSA enhanced the vaccine stability in the powders compared to PVP-containing formulations. However, increasing the BSA concentration increased the hygroscopicity and reduced the dry dispersibility of the powder. No valid mathematical model could be calculated for vaccine stability during production or storage, but the individual experiments indicated that a formulation combining mannitol, inositol and BSA in a ratio of 73.3:13.3:13.3 (wt/wt) resulted in the lowest vaccine titre loss during production (1.6-2.0 log(10) 50% egg infectious dose (EID(50)) and storage at 6 °C (max. 0.8 log(10) EID(50) after 6 months) in combination with a low moisture content (1.1-1.4%), low hygroscopicity (1.9-2.1% water uptake at 60% relative humidity) and good dry dispersibility properties.