Background:
Teenage e-cigarette ever-use has risen significantly in recent years in Ireland similar to trends elsewhere in Europe, the US and Asia-Pacific region, leading to concerns about e-cigarettes promoting experimentation, and progression to current smoking.

Objectives:
We set out to establish a profile of young ever-e-cigarette users by examining individual, peer, and familial associations with ever-e-cigarette use among 15-17-year-olds.

Methods:
A stratified random sample of 50 schools was surveyed in 2019, with 3,495 students aged 15, 16 and 17. Bivariate and multivariable logistic regression analyses were performed using Stata version 16.

Results:
Prevalence for ever-use of e-cigarettes among 15-17-year-olds in Ireland is 37%. Ever-tried cigarettes had an adjusted odds ratio (AOR) of over 4 for ever e-cigarettes use (AOR=4.15, 95% CI: 1.29-13.41, p<.05), ever cannabis use (AOR 2.21, 95% CI: 1.11-4.41, p<.05), and ever inhalants use (AOR=2.51, 95% CI: 1.07-5.88, p<.05). Children with university educated mothers had higher odds of trying e-cigarettes, (AOR=3.46, 95% CI: 1.40- 8.54) p<.05), and fathers not significantly (AOR=2.10, 95% CI: 0.97-4.55, p=.058). Reading books for enjoyment (AOR=0.32, 95% CI: 0.16-0.64, p=.001), a household having rules relating to smoking in the house (AOR=0.53, 95% CI: 0.30-0.94, p<.05), and perceiving moderate risk in using e-cigarettes (AOR=0.20, 95% CI: 0.07-0.67, p<.05) were associated with lower AOR. E-cigarette ever-use, adjusted for covariates, was not significantly associated with gender, age, perceived familial wealth, household composition, academic attainment, sports or hobbies, age of smoking initiation, truancy, peer risk activities /peer support, familial regulation/ satisfaction.

Conclusions:
The marked increase in Irish teenagers' e-cigarette ever-use is part of a pattern of teenage polysubstance use. Several modifiable social determinants were identified including, perceiving risk in e-cigarette use, and living in a household with rules related to smoking. Raising awareness among higher-educated parents, of risk of e-cigarette use by teenagers, may be of benefit.