We can't know what the long term effects of vaping are for definite yet. That said, we obviously can extrapolate from the around twenty years of it being fairly common place. And the one conclusion that can be drawn is that it's a huge harm reduction compared to tobacco in the short to medium term, and extremely likely over any longer term.
One of the big limitations here, or at least a big skew to be aware of, is that most of the data we have on the health of vapers is data on ex-smokers. For instance, COPD is much higher in vapers than the general population, but that's to be expected if almost all your vapers with COPD are of an age where they previously smoked for twenty years or more.
Another thing to consider is that a lot of the elements that have been shown to be likely harmful in vaping have been removed (EU legislation that came into force prior to Brexit). The horror that occurred in the US with a horrible lung condition spreading traced back to cannabis use and the acetates being used to make the liquid - that's not something that's ever been allowed here.
I try to be discreet about vaping but the other thing, for this thread generally, is that there doesn't appear to be passive vaping in the way there's passive smoking. I get it if people don't like the smell or whatever, but at a football ground you're outdoors. There's an awful lot of people in football grounds I hate to have to smell, look at, or especially listen to, but I'm not sure the extent to which my dislike of that warrants a blanket ban. A big part of me wants to say if you're worried about someone vaping nearby then wait till you find out about cars. There are many parts of the world where the cleanliness of the air is a legitimate concern and none of it is because somebody's got a menthol vape.