There is a growing body of evidence that shows that vaping is considerably less harmful than smoking. Public Health England say that vaping is at least 95% less harmful than smoking and Cancer Research UK have found that second-hand vapour doesn’t harm those around you. Many smokers are concerned about so-called ‘popcorn lung’, but diacetyl, the chemical linked to this condition, has been banned in the UK.
The House of Commons Science and Technology committee recently conducted a detailed study on the use of e-cigarettes and heard a broad body of evidence. Their report concluded that e-cigarettes provide a lower comparative harm than tobacco smoking. Their full report is available here