Viruses, and particularly genetically engineered, replication deficient viruses such as adenoviruses, poxviruses, MVA viruses, and baculoviruses which encode one or more antigens of interest, such as TB, malarial, and HIV antigens, are spray dried with a mannitol-cyclodextrin-trehalose-dextran (MCTD) to form a powder where the viability of the viruses are maintained at a suitable level for mass vaccinations after spray drying, and where the viability of the viruses are maintained at suitable level over a period of storage time, even in the presence of humidity.