The system is comprised of an inhaler containing a mix of liquid teflon and a few million reprogrammed Techno-mage nano-virus cells. Once inhaled the nano-virus sits in the lungs and coats anything that comes in, down to 20 microns in size, and sloughs it out of the system. Since the Drakh plague is primarily airborne this works as an effective shield, however it won't help a person who's already been exposed.
While did represent a significant step forward in combating the plague, it was not without its limitations. Since this is essentially adapted from salvaged techno-mage technology, the virus has a built in loop that periodically requires new instructions and without the technology to broadcast new instructions, the re-programmed nano virus reverts in an inert state. So after roughly 48 hours a person would again become susceptible to infection. In addition, repeated use of the shield within a short space of time was likely to cause some very unpleasant side effects and without a way to manufacture more nano cells there was a finite number of times the shield could be used.