Dr Dana Meaney-Delman, head of the CDC team investigating the outbreak has reported that “We've narrowed this clearly to THC-containing products that are associated with most patients who are experiencing lung injury. The specific substance or substances we have not identified yet”. We need to be clear about what this outbreak is and is not. It is not a problem linked to long-term use of regulated nicotine vaping products. If it were, we would expect to see a very different demographic profile affected, more typical of long term vapers. PHE has not changed its advice on nicotine containing e-cigarettes: Smokers should consider switching completely and vapers should stop smoking. The evidence still shows that vaping carries a small fraction of the risk of smoking. Using a nicotine-containing e-cigarette makes it much more likely someone will quit successfully than relying on willpower alone. But it’s important to use regulated e-liquids and never risk vaping home-made or illicit e-liquids or adding substances.
From Safer nicotine wiki