No it isn’t. Quoting your own source “ Live vaccines contain a weakened or attenuated form of a virus or bacteria.”. That is not what is suggested here.
Intentional infection through controlled means with the contagious virus hasn’t been used since Smallpox (as opposed to pox parties). There is no accepted term. The meaning was immediately clear to me on first reading it. It appears to be a successful reintroduction if a word for an analogous purpose. It’s even unique enough to be googleable.
To me, the Oxford shooting is a cautionary tale of being too sensitive and getting in the habit of expecting everything to be a false alarm.
I have a hard time identifying which steps actually went wrong. Specifically, some of those red flags are only alarming in combination with others, but treating them like problems actually causes too many false alarms that the school has been implicitly trained to ignore. I’d include in this a teenager who is allowed to go shooting, talks about it, posts on social media about it. All of this is perfectly legal and not even unusual in some locations. The teenager having his own handgun is technically illegal depending on interpretation, but a parent buying a gun and keeping possession of it but designating it for the kids use is fine, and kids would refer to it as their gun. And here we see the payoff that the school has been forced to react to all these things over the years when it’s as innocent as if the kid were engaged in any other pastime.
The parents were apparently negligent here. They knew at the time they were called into the office that the kid had access to the gun. That’s information the school didn’t have.
The school should have had it, though. I think when you find a kid drawing violent images, it isn’t in itself a cause for discipline, but it is a reason to ask questions. And a few of those questions should have been “do you have a gun in the house?” “does your son have access to it?”. Those might have been enough to motivate a search.
Even searching ammo online is one of those things against the rules for no good reason. The way zero tolerance policies are often implemented is that the picture of the gun is treated as if it’s a danger. Someone could have been scared by that. The “safety issue” is not actually a safety issue, and everyone knows it but they have to pretend. But then once they’ve gone through the motions, they forget that a kid drawing pictures of killing people might also be an indicator of real violence, not just “I’m offended” violence.