we don't know for sure that it does any damage to your lungs. uma pretty much hit the nail on the head.
that being said, your lungs should not be your only concern. remember that your'e still ingesting nicotine and nicotine is a drug. more than that nicotine IS a toxin. and toxin's are at their core poison. so your'e literally vaping poison. that being said, there have been no proven negative long term effects of taking in small amounts of nicotine over a long period of time.
so, you make your own mind up. i'm going to continue vaping because i personally enjoy it. i KNOW 2 things for a fact.
1.) since i quit smoking and started vaping my 2 mile run time has gone from 16:32 to 13:28. 3 minutes is ALOT of time to take off of a 2 mile run time. so i KNOW FOR A FACT that my lungs have improved since giving up the cigarettes.
2.) i know that vaping is not as healthy as someone who doesn't smoke or vape. but like i said, i enjoy it and my lung function seems to have improved so i'm more than happy to keep on vaping