- Two recent studies grouped some ongoing cigarette smokers under the label “EC switchers,” potentially distorting comparisons.
- In both papers, people classified as using vapes had significantly lower risks of certain major health outcomes than those who continued smoking.
- When complete switchers were analysed separately, effect sizes were similar to those who quit nicotine entirely, but small sample sizes limited statistical significance.
- One study recommended against switching despite reporting similar risk reductions to complete abstinence.
A new critique has raised concerns about how two recent health studies defined “switching” from cigarettes to vapes – and whether that definition could influence how the findings are understood.
In a post titled “New Research Flaw Unlocked?”, behavioural scientist Arielle Selya, PhD, reviewed two Korean studies that analysed national health insurance data. Both followed patients who smoked cigarettes and had serious health conditions at baseline.
Researchers then compared health outcomes roughly five years later, based on whether participants continued smoking, used vapes, or quit nicotine entirely about one year after baseline.
The first study examined patients with chronic obstructive pulmonary disease (COPD) and tracked outcomes including lung cancer, COPD exacerbations, major adverse cardiac and cerebrovascular events (MACCE), and all-cause mortality. The second focused on patients with hepatitis B and tracked the development of hepatocellular carcinoma, a form of liver cancer.
The definition of “switching”
According to Selya, the central issue lies in how the studies defined “EC switchers.” She wrote: “The critical flaw is that the ‘EC switchers’ group still includes cigarette smoking.”
She added: “‘Switched’ usually means they switched completely away from cigarettes. Here, it doesn’t mean ‘fully switched,’ or even ‘mostly switched’; it just means they used e-cigarettes, and they don’t distinguish from people who switched completely versus dual-used.”
In other words, some participants categorised as having switched were still smoking cigarettes as well as using vapes. That means the “switcher” group may have included both complete switchers and dual users.
Dual use can carry ongoing risks associated with smoking. Grouping these participants together with complete switchers could make it harder to see differences between people who stopped smoking entirely and those who continued to smoke.
Selya also suggested it was unclear whether the starting sample included only exclusive smokers, writing that “It’s hard to tell because the sample inclusion criteria aren’t described thoroughly.” If some participants were already dual users at baseline, that could further complicate comparisons.
What the studies found
Despite the grouping issue identified in the critique, both studies reported statistically significant reductions in certain major health risks among participants classified as using vapes compared with those who continued smoking.
In the COPD study, participants using vapes after one year had significantly lower odds of major adverse cardiac and cerebrovascular events at five years (adjusted hazard ratio, AHR = 0.80). Those who quit nicotine entirely showed a similar reduction (AHR = 0.85).
Other outcomes in the COPD study, including COPD exacerbations and all-cause mortality, did not show statistically significant differences.
In the hepatitis B study, participants using vapes after one year had significantly lower odds of developing liver cancer (AHR = 0.78), which was the same magnitude of risk reduction observed among those who quit nicotine completely (AHR = 0.78).
Separate analyses of complete switchers
Selya noted that additional analyses in the COPD study separated complete switchers from dual users. These analyses did not reach statistical significance, which she attributed to small sample sizes and wide confidence intervals.
However, she wrote that “with the exception of lung cancer, all other outcomes have a similarly-sized reduction for complete switchers and complete nicotine abstainers.”
The critique also questioned how non-significant results were described. In the COPD paper, she wrote that non-significant findings were characterised as “not providing comparable.. benefits” compared with quitting.
In the hepatitis B paper, the authors concluded: “Complete tobacco cessation should remain the primary strategy given superior behavioral sustainability, with no significant difference in HCC risk reduction versus switching.”
Selya summarised this as: “Switching to ECs was associated with the same risk reduction in liver cancer as complete nicotine abstinence, but we recommend against switching to ECs because it’s not as stable/sustainable.”
The hepatitis B paper also reported that only 12% of those classified as “EC switchers” eventually quit smoking, compared with 61% of those who initially quit.
Peer review and presentation
The critique noted that analyses of complete switchers in the COPD paper appeared in red font in a pre-formatted version of the manuscript, suggesting they may have been added during peer review.
Selya described this as “a success of peer review because the paper would have been almost completely uninformative without it.”
She concluded by warning that terminology matters in research and reporting. She wrote that sometimes “ ‘EC switchers’ means ‘EC switchers and dual users,’ in future research and in any media coverage these studies get.”
The analysis highlights how definitions and grouping decisions in epidemiological studies can shape the way findings are presented – and how careful scrutiny of study methods is essential when interpreting research on smoking, vaping and long-term health outcomes.
