I'd go back to all PG if I were you. My Pulmonary doctor couldn't believe people were really vaping VG. He said get off it and get off now. He was very animated for an otherwise mild mannered guy. He said vaping VG is just like coating your lungs with oil. Needless to say, no more VG for me.
This person's reaction is understandable but seems to indicate a lack of knowledge of the issues. Glycerine is not an oil and is approved for inhalation in pharmaceuticals, and is apparently being used more frequently for new medical inhalers than PG is. PG is still used in some asthma inhalers, and for the nebulizers used by lung transplant patients, though perhaps because its bactericidal and virucidal performance is outstanding as much as anything else.
Dow Chemical make all possible grades of PG and VG, and advise that their synthetic (not vegetable) glycerine is the best choice for inhalation.
OPTIM - The OPTIM Advantage | The Dow Chemical Company
OPTIM - The OPTIM Advantage | The Dow Chemical Company
In fact they advise that glycerine is chosen for inhalation, not PG.
Also, Intellicig were the first manufacturer to produce glycerine-only e-liquids, and their materials and facility are overseen by university staff advised by international academics. If glycerine were not a good choice for inhalation they would not be using it.
There are 70 years of research data on the inhalation of PG, and one fact is that no one has ever been shown to have died from inhaling it or even ingesting it in large quantities. It can also be injected into the bloodstream without incident (it's used for injectable medicines, where the drug does not mix with water). Some are intolerant to it, but that would apply to just about anything. There is far less research on the inhalation of glycerine but current feeling seems to be that it is just as safe, and has less potential for tolerance issues. Dow would not back it if there were any chance of its safety profile being debatable.
So on balance, 'VG' is at least as safe as PG but if you wanted to avoid colds, flu, or even some real nasties in the atmosphere, PG might be a better choice, since although Optim glycerine is described by Dow as having bactericidal properties, it is generally recognised that PG has outstanding capabilities in this area.
On a personal note I've vaped 100% VG for several years and my lungs have never been clearer. The choice of brand might be important though, there is far more potential for variance in quality or suitability for purpose in VG than in PG.