This is an AU of the infected!AU. It's complicated, just don't worry. In which both Leon and Helena are infected, due to their exposure to the C-Virus.
Chrysalis
"Oh my God," said Helena. She took a step nearer, still not sure if she was just having a nightmare, or if this was reality. She lifter her gun, and let it drop to her side again. She could feel the tears welling up in her eyes. Deborah had done it—now Leon, too? She buried her face in her hands, and the events from moments before played over in her mind.
The large B.O.W. had been waiting for them when they had landed in China, and Jake and Sherry had faced it with them. It was terrifying and large, bigger than any of the B.O.W.s Helena had seen before. It had taken a large supply of ammo to take it down, and her breath was short after having to breathe so much of the noxious gas that had been wafting around the airplane. It had gone down, though, finally. She had gone to Sherry, and tried to find out what was going on, or at least what they knew about it. It was then that she heard the grunt from behind her.
Helena had whipped around to see Leon kneeling to the ground in fatigue. Helena knew that it had been a trying past 24 hours, but now wasn't the time to take a rest—and Leon would know that. Jake held a hand out to him, but instantly withdrew it when he saw what was happening.
Before their eyes, Leon was becoming encases by a chrysalis. "Leon!" shouted Helena. He did not move or make any indication that he had heard her. Sherry was unable to make a sound. Jake joined Sherry and Helena, and Helena's hand went to her gun. She couldn't believe what she was doing as she unholstered it and held it up, pointing it at the nearly fully cocooned Leon. "Oh my God," she said.
"Helena," said Sherry, breaking Helena from her thoughts. "What are you doing?" There were tears on her face, and her eyes darted frantically from Helena's gun to Leon to Helena's face, and back again to the gun.
Helena's thoughts now flitted to Deborah. The same thing had happened to her: the chrysalis, the mutation, the damned virus. Helena wiped tears from her eyes and mucus from her nose with her arm, unaware previously that they were even there. She steadied the gun in her shaking hand and kept it pointed at the now fully formed cocoon.
"I'm sorry," said Helena. "But we all know what has to be done." Her finger quivered on the trigger for a moment, and she turned away, squeezing her eyes shut as she pulled the trigger, feeling the shot's vibrations as they traveled through her body, knowing that she'd relive them over and over again, in countless nightmares that she'd doubtless have about this day. When she did open her eyes, she did it slowly, and turned to Leon's cocoon.
To her surprise, it was still there, in fully stature. Helena pulled the trigger again, and it simply clicked. The gun was empty. She felt at her belt and found no new clips. She turned to Sherry and Jake. "Sorry," said Jake. "I've got nothing." Helena turned back to the chrysalis and ran to it, striking it over and over again with her gun. A soft clank came from the strike, and Helena did it again, whacking her hands and gun against the shell. Her body was shaking, heaving with her sobs, which descended into a coughing fit.
Sherry stepped forward to comfort her, but then took a step back. "Oh my God," said Helena, looking at Leon's new form, incubating until he emerged as who knew what.
Sherry and Jake could have said the same thing, though, because at that moment, the same sort of chrysalis began to creep its way around Helena's body, though she didn't seem to notice. Her eyes were locked on Leon's cocoon as she was engulfed.