Nicotine is known to be not significantly addictive (similar to caffeine).
Vaping is known to be a very low health risk to the vaper and the risk to other people is insignificant. These risks are unlikely to change over time.
There is no reason to associate vaping with smoking – the are not the same.
There is no reason for the WHO to be concerned with vaping and e-cigarettes as they are not a health hazard. On the contrary, they are a significant benefit if a smoker chooses to switch to vaping.