Strain B

Sinister decided for Strain B, mainly because he was curious about who would get hit initially and how they would react.

There had been one little problem initially: he needed someone on the inside that could spread the virus.

Sinister briefly mulled over it, until he settled on someone who had, a while back, piqued his interest.

He'd kept someone in the back of his mind from the few, brief encounters they'd had.

No one noticed it, but it was clear to Sinister that this person was resentful of their low place on the X-Men's totem pole.

He managed to get into contact with him and made him a deal: Help test the chemical on the X-Men and, in return the potential traitor would get whatever they wanted.

Both sides would benefit from the deal: Sinister would be able to study the effects on the X-Men (always a source of interest for him) and the traitor would use Sinister's chemicals (and a promise for some future help to isolate the traitor and their target) to get someone they had long lusted after.

That got the traitor to instantly agree.

As such, it was in everyone's best interest that everything went perfectly.

The traitor was instructed to lay low until the time was right as the virus had to be just right.

It took Sinister a long time, but he eventually managed to make sure. the chemical was undetectable so not even Wolverine would smell it and no one would ever know that they'd been hit by it, not even after they began to feel the effects of the virus.

And on a team like the X-Men, those effects would be absolutely devastating.

Granted, it would work slower than Strain A, but that was fine with him, it gave the virus more time to spread without anyone realizing it.

Sinister thought about how, even among other superhero teams, the X-men were notorious for having barely repressed attractions towards one another and this would push plenty of people over the edge and into making bad decisions that would tear the team to shreds.

The effects had been tested on a few random people that Sinister had kidnapped and things had gone very well before, but this was the X-Men a they had a tendency to undo even his best plans and if one thing were to go wrong then he and the traitor would be in a hell of a lot of trouble.

Still, he had to move forward with this plan, so first thing was first for Sinister, he made sure his mole set up video cameras everywhere so that he could easily study how everyone reacted to the virus.

With everything set up, Sinister sent word to his mole that it was time to expose the X-men to the chemical.

If every thing went well, the X-Men would never be the same and, more importantly, they'd never pose a threat to Sinister ever again.