Dark Shadows #20 (Dark Shadows: The Complete Series

Dr. Julia Hoffman injects the vampire Barnabas Collins with a blood serum which "only balances [his] system temporarily." She is unaware that her patient's cousin Quentin Collins also suffers from an unspeakable curse. When Quentin transforms into a werewolf in front of Julia, she stabs him with the closest weapon, a hypodermic filled with Barnabas's "blood serum." Now, Quentin becomes a vampire under a full moon!