The nano-virus shield was a counteragent system developed by Dr. Sarah Chambers of the Excalibur to temporarily protect and individual from infection from the Drakh plague. 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.