Old Nick is Saint Nicholas' elder brother.
He sees his brother's good work at Christmas and wants to help in his own way, and sees a gap in the market (he really can't compete with spreading good).
The naughty list
Saint Nicholas neither punishes or rewards kids on the naughty list, but Old Nick decides that he wants to do something about that.
So, he hoodwinks and bribes a few elves in the chemical factory and makes them create a genetically-targeted virus that chemically sterilises bad kids.
The creation of the genetic target is outside the scope of this question (suffice to say that a combination of genetic markers have been identified). The virus is harmless to and does not infect normal people. Normal people can only act as carriers in the physical sense.
Now that Old Nick has a stockpile of modified flu virus, he's now stuck with the logistics of deployment.
Santa's security measures on his reindeer barn means that Old Nick cannot steal the sleigh, he must use conventional methods. Having said that, he has the luxury of preparation time and unlimited funds.
How is he able to spread the virus as quickly and widely as possible on the night of the 24th December?