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Some people who switched to vaping as a way to give up smoking still regularly used traditional cigarettes because of a strong attachment to and nostalgia for the "real" thing, the study found.
This included emotional attachment to the ritual of smoking, and perceptions of vaping as inauthentic.
The research, published in the international journal Tobacco Control, involved interviews with 20 vapers who still regularly smoked cigarettes about why they did not make the full transition to vaping.
"Many started their quit attempt expecting that vaping would offer them exactly the same experience as smoking. However, they often became disappointed when their experiences didn't replicate smoking, and continued smoking as well as vaping," lead author Dr Lindsay Robertson said.
The study found it was important to manage smokers' expectations more carefully and concluded good advice from well-trained retailers with specialist vaping knowledge would be useful.
Professor Janet Hoek, who lead the Health Research Council funded project, said that advice would be important because some people thought cutting down the number of cigarettes smoked was a successful outcome so stopped trying to quit smoking completely.
But, a study published in the UK last week showed smoking only one cigarette per day was far more harmful than previously expected - the risk of developing heart disease or having a stroke was still about half that of someone who smoked 20 a day.
The Otago study also found that some people only switched to e-cigarettes or vaping because it was cheaper and more convenient than smoking as the price of cigarettes increased and restrictions around where smoking was allowed became tighter.
The researchers concluded that government legislation could help people make a full transition away from smoking to exclusive use of e-cigarettes and vape devices, if it was done right.
Chief executive of public health service Hāpai Te Hauora Lance Norman said while there was a consensus that electronic nicotine delivery systems were less harmful than cigarettes and were helpful for those trying to give up smoking, the new research showed more support was needed for those trying to give up.
"These findings suggest we need to support our whānau in this transition with realistic expectations, and informed, well-trained health professionals. We know from the extensive work done in New Zealand on tobacco addiction that no single intervention will be a silver bullet, one size fits all solution for everyone," he said.