A study measuring the aerosols from two vape users and comparing it with secondhand cigarette smoke found vapes produced a much lower level of ultrafine particles, but a much higher level of nanoparticles. It is not clear what risk these pose. Another study found vape use increased fine particles in a room’s air.

From SMH: Is secondhand vaping a growing threat or ‘fake news’?

It would seem the science is still not in on just how dangerous it is, but further in the article it says:

The question, says Demaio, is whether we should wait for conclusive evidence before taking action.

“We don’t have any long-term studies on the safety of these products, or on the safety of secondhand exposure. It took us 20 years to realise it [tobacco] was causing damage in the next generation of kids who were living with others who smoked.

“My worry is we take another two or three decades to realise the same thing.”

Not as far as I’m aware, but vapes can also contain different chemicals that may contribute towards different types of health conditions. More research is needed on the long-term effects I think (which can only come with time). One thing I have definitely noticed among people I know who vape and/or smoke is that the vaping is constant and done everywhere and anywhere, whereas smoking is far less common and will be something that people remove themselves from a group to do (outside and further away). Vapers are far less considerate of others and vape more because they believe it’s less harmful, which increases the level of harm. So in that sense, I think government policy is also important here to signal that vaping is not harmless so that we can start changing the culture around it like was done with smoking many decades ago.