It's been known for over 1/2 a century that smoking leads to frequent sore throats and colds.... Smoking interferes with the vitamin C absorption and therefor the proper functioning of the immune system. I got totally sick of getting 3 or 4 nasty colds every year and so I started taking massive, daily, amounts of vitamin C (when I was still smoking).... After that I went for almost 8 years without getting one single cold (while still smoking)...
Sorry, and not that it matters, but I do not agree that vaping improves one's health or makes them feel better.......... Years ago, b4 vaping was ever invented, I had talked with many folks who quit smoking........ In every single case, the people told me how much better they feel after quitting.... It's highly unlikely that vaping helped those people in the past since vaping did not exist at that time... A more logical conclusion would be that all of the toxins eventually left their system, their lungs started to repair themselves, and they got more oxygen to their brain and other vital organs.
As for vaping helping reduce the frequency of colds, I have no comment in those regards.... My wife makes her own concentrated herbal oils and she always carries a small bottle of lavender oil with her and she constantly sniffs it throughout the day because it eliminates contracting upper respiratory disorders such as colds/flu's ... Since she started breathing the fumes in from the lavender oil, she has not had a cold or flu in over 10 years... This is because lavender has anti-microbial properties to it.... So, there may be merit to the thought that anti-microbial properties of PG help the body to fight off respiratory infections.... But that is a long way from improving one's overall health or experiencing the vigor one has after quitting smoking.