let's cross fingers this doesn't become the obvious "vaccine manufacturers are spreading viruses" that anti-vaccine conspiracy theorists need.
Well, considering the historical behavior of for profit enterprises, it's not something that would be beneath them.
If it wasn't for tight regulation and the huge media backslash they'd be pouring the stuff by the tons. But in any place/country/era where they could bypass such stuff, businesses have done so.
There's no reason you need more than a handful of people to be deliberately evil. Plenty of people will follow them unknowingly or under the threat of losing their jobs.
But in the case we're talking about it's even easier. For one, it doesn't have to be "many thousands of people" working in the company. Just a few, entrusted by the upper echelons. In the same way that companies historically employed thugs, mafia etc, to beat and even murder union members and strikers. It's not like it was something openly decided in a company meeting. Usually it takes the form "take care of the problem, the less I know the better" from some superiors (with an implicit knowledge of what that entails).
Single employees, no matter how senior they are, shouldn't be able to perform an action like this. There's got to be systemic gross incompetence to even allow a single employee opportunity to access a large batch of fatal disease carrying material without oversight. I doubt very much this was a case of "oh the intern threw out the wrong barrel of disease, shucks".
Given that most people are effectively vaccinated for polio, I can see this plant being not quite so strict.