Antiviral follows the story of Syd March, an employee at a clinic that sells injections of live viruses harvested from sick celebrities to rabid fans who wish to partake in the ultimate form of communion. Syd supplements his income by selling illegal samples of these viruses on the black market, smuggling them out of the clinic in his own body. When he becomes infected with the disease that kills superstar Hannah Geist, Syd becomes a target for collectors and obsessed fans. He must unravel the mystery surrounding the starlet’s death before he too meets a morbid end.