AIMS: To investigate whether effects of the ASSIST (A Stop Smoking In Schools Trial) school-based smoking prevention intervention diffused from students to the people they lived with. DESIGN: Secondary analysis of a cluster randomized control trial (cRCT). SETTING: England and Wales. PARTICIPANTS: 10,730 students aged 12-13 years in 59 schools assigned using stratified block randomisation to the control (29 schools, 5,372 students) or intervention (30 schools, 5,358 students) condition. INTERVENTION AND COMPARATOR: The ASSIST intervention involves 2-days of off-site training of influential students to encourage their peers not to smoke over a 10-week period. The control group continued with their usual education. MEASUREMENTS: The outcomes were the proportion of students who self-reported living with a smoker and the smoking status of each resident family member/caregiver. Follow-up assessments were immediately after the intervention and at 1 and 2 years post-intervention. FINDINGS: The odds ratio for living with a smoker in the intervention compared with control group was 0.86 (95% confidence interval 0.72, 1.03) immediately after the intervention, 0.84 (0.72, 0.97) at a 1-year follow-up, and 0.86 (0.75, 0.99) at a 2-year follow-up. In a three-tier multilevel model with data from all three follow-ups, student-reported smoking by fathers (OR = 0.90, 95% CI 0.80, 1.00), brothers (OR = 0.78, 95% CI 0.67, 0.92), and sisters (OR = 0.80, 95% CI 0.69, 0.92) was lower in the intervention compared with control group. Sub-group analyses by baseline smoking status suggested these effects were more consistent with prevention of uptake than prompting cessation. CONCLUSIONS: The ASSIST (A Stop Smoking In Schools Trial) school-based smoking prevention intervention may have reduced the prevalence of smoking in people who lived with ASSIST-trained students. This indirect transmission is consistent with the predictions of diffusion of innovations theory which underpins the design of ASSIST.
Smoking, diffusion, family, peers, prevention, spill over