BACKGROUND AND AIMS E-cigarette and other electronic nicotine delivery systems (ENDS) use has grown considerably over the past decade, with notable increases among young people. US state policy contexts for ENDS and tobacco may shape initiation into ENDS use among adolescents as they age into early adulthood. We aimed to determine whether state-level comprehensive vaping ban policies reduce the odds of youth initiation into ENDS use, net of additional state-level ENDS and tobacco policies, as well as the youth's cigarette smoking status.

DESIGN Longitudinal data from the Population Assessment of Tobacco and Health study were merged with a state-year database on tobacco and ENDS policies. Multivariable discrete-time event history models of ENDS initiation were estimated.

SETTING United States.

PARTICIPANTS Twenty thousand twelve youth assessed over six waves from 2013 to 2019 (n = 53 974 observations).

MEASUREMENT We examined comprehensive indoor vaping bans (i.e. 100% vape-free workplaces, restaurants and bars) as a key factor in initiation into ENDS use (i.e. first instance of vaping) from age 13 to 22.

FINDINGS Among young people, residing in a state with a comprehensive vaping ban was associated with 18% lower odds of ENDS initiation (odds ratio = 0.82; 95% confidence interval =[0.71, 0.94]), even after controlling for other state ENDS and tobacco policies, the youth's cigarette smoking and socio-demographic background and state-level covariates.

CONCLUSIONS In the United States, state-level vaping bans (i.e. 100% vape-free workplaces, restaurants and bars) are associated with reduced odds of youth initiation into electronic nicotine delivery systems use.