Albert Wesker, father of Jake Muller, had a very rare physiology. His body was highly resistant to viral infection, and he was even able to manipulate the virus he had injected into himself so that he would only reap their benefits and none of its deleterious effects. This self-experimentation gave him abilities that can only be described as superhuman.
As Albert's son, Jake enjoys the same immunity to viral infection. When Jake injects himself with a solution containing the C-Virus, it has no visible effect on him.
Albert Wesker planned what would have been the deadliest terrorist attacks in human history, and he would have succeeded had Chris Redfield and the BSAA not killed him in time.
Jake has never met his father and knows nothing about the atrocities he committed. He is also unaware of the genetic legacy he is heir to.
While Jake was being imprisoned in China, he wrote down his thoughts on a whim, including some thoughts on his father.
It's been about 2 months since being caught. I think I've started to pick up enough Chinese to know what some of these Neo-Umbrella guys are saying. They keep talking about my dad. I even heard the lady who gives out the nutritional supplements talk about him. I guess Albert Wesker really is my dad, and he really did try to kill everyone on the planet. Fuck.
I bet Sherry knows and that's why she needs me. Why wouldn't she tell me? Jesus Christ, my head hurts just thinking about it.
Albert Wesker, the father of Jake Muller, possessed an extremely rare genetic makeup. Not only was there a resistance against various viruses, he conversely injected himself with a virus and was able to only take the virus' advantages and strengthen his body tissues.
Therefore, even though Wesker's son Jake directly injected the C-Virus, his tolerance to strong viruses was inherited by Jake.
Wesker planned global-scale bioterrorism and was killed by the BSAA, led by Chris Redfield. Jake himself has not met his father and does not know his identity either.
While Jake was living in forced confinement in China, he wrote about his complicated state of mind regarding his father on a whim.
"It's been about a month or two here since we were captured. Recently, I've finally come to understand Chinese, which those Neo Umbrella guys speak. They keep talking about my father. I've heard them indirectly, and I even heard the lady who gives out the nutritional supplements; the story is that Albert Wesker is my father and unfortunately, it seems she's serious.
Somehow or other, it seems it's true that Wesker was a monster who tried to destroy the world. Well, such an asshole was my father. I can't even laugh. Sherry probably knew and that's why she approached me. Why didn't she tell me?