Um, yes, yes they do and yes it does happen, even if you weren't on antibiotics or forgot to take it. Bad bad comparison to attempt to use.
It's incredibly rare, which is the point. Transmitting Covid while vaccinated is also incredibly rare, as the evidence in the article shows.
The IIHF should have taken the same approach the NFL is currently taking, because if they were going to force teams to forfeit for any positive test then the tournament was always doomed to fail.
It was predictably going to turn into a joke and already has.
I suspect they will feel pot committed and try to salvage this by making the knockout stage a full on bubble, but it's already too late.
When teams start forfeiting knockout games, or god forbid, the gold medal game, this will look even worse.
They should either cancel the tournament, or change their forfeit rules so they aren't so ridiculous.