Development of a dried influenza whole inactivated virus vaccine for pulmonary immunization

Stabilization and ease of administration are two ways to substantially improve the use of current vaccines. In the present study an influenza whole inactivated virus (WIV) vaccine was freeze-dried or spray-freeze dried in the presence of inulin as a cryoprotectant. Only spray-freeze drying rendered powders compatible with administration to the lungs by insufflation. Pulmonary administration of the powder vaccine obtained by this method to BALB/c mice led to a transient influx of neutrophils and a concomitant decrease in the number of macrophages as did administration of liquid vaccine. Inflammatory reactions to both vaccines were mild and short-lived. Immunization studies showed that the immunogenic properties of WIV vaccine were not affected by drying. Pulmonary administration of the powder WIV vaccine induced a systemic immune response of the same magnitude as liquid vaccine while mucosal IgA responses were higher for powder WIV. In a challenge study where immunized mice were exposed to a lethal dose of live virus, two pulmonary doses of either liquid or powder WIV vaccine were equally effective as a single intramuscular injection of subunit vaccine in terms of reduction of the viral load in the lungs. To conclude, in the models employed for these studies the use of a dry powder WIV vaccine for pulmonary immunization was shown to be safe and efficient.