In response to Alexia, Birkin obsessively searches for a way to eradicate the ~10% of people immune to Spencer's t-Virus. He creates the Hunter and other B.O.W.s to clear away survivors rather than create a strain that can infect everyone, which he can't do.
Researchers at the Arklay Laboratory ponder if more success would be achieved if Alexia was present, which annoys Birkin immensely. Birkin moves too fast in his research for the specimens to survive, much to Wesker's annoyance. Yet Lisa Trevor survived all that she was infected with. Wesker questions how she can survive such exposure to so much of the virus.