Alien- Infection Control

It dragged one of the staff behind it, a muscular bald man. The claws of its right hand gripped the collar of the man’s blue smock. The man was infected with cellular necrosis, but he had far fewer lesions and blemishes than the others they’d seen, and no apparent wounds. The doctor thought the man might be dead, but then he rolled his head from side to side. His eyes fluttered several times, but did not open. Why wasn’t this man more seriously affected?
…

This explained why the man’s case of cellular necrosis was so mild. The Xenomorph was able to control the strength of the contagion. It wanted its progeny to possess the same strengths it did, but it also needed the host to live long enough for an embryo to be implanted and gestate. It seemed impossible, but absolutely fascinating.

Prototype, Chapter 17