O2STK is in possession of an anti-vampire vaccine. It is also called the "Von Tessie Formula", presumably after the Middleman who invented it.
The vaccine is blue in color and delivered by injection. Once administered, it prevents a human being bitten by a vampire or to halt the process of transforming into a vampire. However, the vaccine can do nothing about the fact that the vampire now knows his victim's entire life story.
The only known recipient of the vaccine is Clarence Colton, who received it after being bitten by Vladdy.