As you carefuly picked up the last antidote and administered it to Nicole, you took your time to look at her assailant, it was a serpentinewoman, you looked back at Andrea, who was comforting her sister, as you finished the injection, you gently ripped open her pants and shoes, if she was gonna turn into a serpentineman, those two would probably make the transformation more painful.
"What are you... graagh!" started Nicole, before being interrupted as she felt her muscles grow, with each breath and heart beat, she became more muscular, although not as muscular as you, Andrea ripped open her shirt and bra, only leaving what was left of her lab coat, revealing how Nicole's breasts vanished due to the expanding muscles and size.
She then looked at her newly developed claws, they were sharp and powerful, which could cut through most objects, then scales traveled up ber now muscular arms, Nicole tried to stand up, but she instantly fell down as her legs and feet went limp, "I-I'm fine sis..." she panted, before laying on a nearby wall, Andrea moving away from her transforming sister, the two of you watched as Nicole's legs were pulled together, before seemingly merging, the same dark green scales you and Andrea had developing as well, until Nicole developed a long and muscular serpentine tail.
You then heard her moan as the scales reached her clit, just like your transformation, it became an horizontal slit, where from it, two distinct rods emerged, shaping themselves into throbbing reptilian dicks, instantly climaxing the first load of snake seed.
She, or rather, he slowly stood up, awakwardly so due to his new anatomy, he used a nearby table for leverage, before he involuntarily thrusted his hips, letting out another load of snake seed, it didn't take long for Nicole to start stroking one of his new phalluses, accelerating his changes, you and Andrea watched as the scales traveled up to his chest.
He let out a final human moan as he climaxed again, this time on a nearby wall as his hair slowly disappeared, the scales traveled up to his neck, then to the rest of his face and head, his mouth was forced open, revealing how his tongue changed into a long and forked one, while the rest of his teeth vanished, only leaving two large and pointed fangs behind, dripping with a specific substance. Then lastly, his face shifted and pushed, changing into something similiar to the head of a cobra, his nose vanishing as two nostrils were left behind.
Nicole, now a fully transformed serpentman slowly calmed down, before awkwardly slithering away from his mess, letting out a confused hiss as he looked at you and his sister, who almost instantly jumped for a hug, the two of them seemingly smiling as they embraced, you let out something similar to a sigh out of relief, the antidote worked again, you then walked over to pick up Nicole's ID card, giving another glance to the reptilian siblings.
The three of you then left the security room, the three of you wondering what to do next, you had no antidotes left to use if you came across another infected civilian, you could return to a nearby lab and create more of the antidotes, but by now, the military was surely on their way.