In Shades of Red, the vampire plague or OVC (Osculans Vestri Carorum) - Latin for "kiss your loved ones" is based on the virus HIV and measles. I love history, and there's a rich history behind measles, and it's subsequent vaccination. I also love science, which is why I chose HIV; It's new and pretty unique which is one of the reasons why it's so deadly and taken us almost 40 years to--I don't want to say cure--but scientists can make the virus virtually undetectable in sufferers of the disease now.
HIV works on a protein in the immune system. When you contract the disease, it's like your house is burning down, but all the tools you need to fight the fire are inside your house-inaccessible. Also, HIV is new to the human immune system which is why our bodies don't immediately recognize it as a threat. So, when our bodies do begin to fight it, it's too late, our defenses are already compromised.