The use of e-cigarettes and the drop in smoking rates in the US are directly related.

British Medical Journal

Zhu S et al., ‘E-cigarette use and associated changes in population smoking cessation: evidence from US current population surveys,’ British Medical Journal, 2017; 358.

The rapid growth of vaping among adult smokers in the US brought a statistically significant decline in smoking rates.
To determine whether the rising popularity of vaping in the US has an effect on successful quit efforts, the study looked at the quit rates among adult smokers over the age of 14.
Around 2010, vaping in the US started to catch on, and by 2014, it had significantly increased. Data from five national demographic surveys conducted between 2001 and 2015 were used in the study.
In the 2014–15 poll, 22,548 of the 161,054 participants were still smoking, and 2,136 had recently given up. E-cigarettes had been tried by 49.3% of recent quitters, and 19.0% were still using them today.
Key findings:
- Vaping smokers were 62% more likely to attempt to stop smoking than non-vaping smokers. Compared to two out of five smokers, two out of three “dual users” have attempted to stop smoking (65% vs. 40%).
- Smokers who used e-cigarettes had a 70% higher chance of quitting than non-users (8.2% vs. 4.8%).
- The rise in e-cigarette use was accompanied by a record-breaking decline in smoking rates in the US. All other survey years had a much lower quit rate than 2014–15.