Cited in Australia Tobacco Harm Reduction Association:

Large studies have shown that daily vapers are 3-8 times more likely to quit than those not using vaping products (see here and here). National surveys have reported that many millions of smokers have quit by vaping, over 6 million in the European Union, 2 million in the United Kingdom and 2.6 million in the United States. According to the UK Royal College of Physicians, randomised trials with early models have shown that vaping approximately doubles the likelihood of quitting (p103)– however modern devices are more effective .