The Oxford team showed that it could preserve the two vaccine viruses by mixing the viruses with sucrose–common table sugar–and trehalose, a sugar found in plants and mushrooms and used as a stabilizer in processed foods. The team then dripped the mixture onto a membrane made of glass fibers and dried it at room temperature in a low-humidity chamber. This allowed the sugars to form a noncrystalline solid around the fibers of the membrane, immobilizing the virus so that nothing could interact with it. Cottingham notes that neither using sugars nor drying are new ways to stabilize pharmaceuticals. “The crucial step is that the drying happens on the membrane, so we can remove the water at a relatively low temperature,” he says. The exact concentrations of sugars and the type of filter used had to be established by trial and error. “There was a pretty big empirical element in all this,” says Cottingham.
To release the vaccine, the researchers flushed the membranes with saline, which dissolves the sugar almost instantaneously. Based on tests done in mice, the team found that they could store the two different vaccines on sugar-stabilized membranes at a tropical 45 °C for as long as six months without any degradation. The vaccines could be kept for over a year and more at body temperature–37 °C–with only tiny losses in effectiveness.
Nova Bio-Pharma holds the patent on the drying technique, and it has also developed a small, plastic cartridge into which the filter is sealed. The cartridge has a hole at either end, one of which fits a sterile syringe and the other a disposable needle. When the vaccine is administered, a nurse or technician would pass sterile saline through the cartridge, pushing it out slowly. This instantly rehydrates the vaccine.
Samodh de Costa, the stabilization project manager at Nova, says the company already has an aseptic manufacturing process in place that can produce quantities that would be needed for clinical trials. The next steps are to show that the process can be scaled up to industrial manufacturing levels and demonstrate that it works with a standard or newly licensed human vaccine.