Trends in smoking prevalence among 14-15-year-old adolescents before and after the emergence of vaping in New Zealand; an interrupted time series analysis of repeated cross-sectional data, 1999-2023.

Background: New Zealand experienced a prolonged period of minimal regulation on e-cigarettes until the passing of the 2020 Smokefree Environments and Regulated Products (Vaping) Amendment Act. Methods: Interrupted time series analyses of the Action for Smokefree 2025 (ASH) Year 10 Snapshot Survey data from 1999 to 2023 to compare changes in smoking trends among 14-15-year-old students (n = 690,470) before and after the advent of vaping in New Zealand (around 2010). Findings: The prevalence of daily-vaping increased from 1.1% in 2015 (the first year the question was asked) to 1.8% in 2018 before rising to 10.0% in 2023, a nine-fold increase over eight years. From 1999 to 2023, considerable declines in ever-, regular-, and daily-smoking prevalence were observed. However, the rates of decline in ever- and regular-smoking slowed significantly from 2010 onwards (p < 0.001 for both), coinciding with the advent and rapid growth of vaping among New Zealand adolescents. In contrast, the rate of decline in daily-smoking did not significantly change from 2010 onwards (p = 0.066). These findings were robust to sensitivity analyses, including the use of different time series interruption points (change-years) and controlling for inflation-adjusted cigarette prices. Interpretation: Our findings starkly contrast with those from a previous analysis of ASH data, which suggested that e-cigarettes appear to be displacing smoking among New Zealand youth. Instead, our findings suggest that among 14-15-year-olds, the rapid rise of vaping may have slowed the rates of decline in ever- and regular-smoking, while having little or no impact on the rate of decline in daily smoking. Our findings underscore the importance of effective policy approaches to curb both adolescent vaping and smoking. Funding: None.