Ambient temperature filter dried
vaccine formulations have been proposed to simultaneously achieve thermostability and offer a ready-to-use immunisation device that combines reconstitution and injection.
Vaccine concentration should be uniform at the point of injection, but the uniformity following direct reconstitution of filter-dried
vaccines has not been reported. We present here a study of
vaccine mixing and release following dissolution of filter-dried model
protein and
toxoid antigens within a single syringe, filter and needle unit. Release was better for filters made from glass than
cellulose. Without additional mixing, uniformity was poor and only 41% of input
protein was released from
protein filter-dried onto glass fiber. In contrast, adding a simple glass bead and mixing by inversion, 100% release
antigen solution was achieved, with uniform concentration at exit from the needle throughout a simulated injection. Adsorption onto
alum adjuvant had no detectable effect on
vaccine dissolution and mixing. The uniformity and yield of low doses of
diphtheria and
tetanus toxoid was also improved by mixing, albeit with a lower yield of 60-68%. We conclude that uniformity and mixing should be studied to ensure safety and efficacy of directly reconstituted filter-dried
vaccine formulations.