If Jill was poisoned but did not sustain significant damage, she must collect the serum herself.
If Jill was poisoned and sustained damage, she will fall unconscious and Barry will collect it for her. She will regain consciousness in the 1F chemical storage room.
If Chris is poisoned, he will lose consciousness and the player will take control of Rebecca, who must collect the serum for him.
In the original version, if Chris decides not to take Rebecca with him after meeting her in the chemical room, she will automatically take him back there and administer the serum.
The serum is found in a storage room at the Antarctic Base. This serum was created as a cure to Nosferatu's poison, which cannot be cured by blue herbs. Chris will only get it if Claire was poisoned by Nosferatu during the fight on the helipad.
Another serum was used by Dr. Cameron when she was infected by the t-Virus. The serum cured her, but it also had some mixed effects.