Children Learning About Second-hand Smoke (CLASS III): Cluster randomised controlled trial of a school-based smoke-free intervention in Bangladesh and Pakistan

Exposure to second-hand smoke from tobacco is a major contributor to premature death and disease, especially among children. We conducted a two-arm, cluster-randomised open-label superiority trial in Bangladesh and Pakistan to assess the effectiveness of a complex smoke-free intervention (SFI) in reducing children’s second-hand smoke (SHS) exposure. SFI included six awareness-raising sessions, including a children's performance, a smoke-free home pledge and achievement certificate. Between June 2022 and January 2023, we enrolled 2,751 year-five students from 74 schools; 37 schools (1,407 students; 633 boys, 774 girls) were assigned to SFI, and 37 schools (1,344 students; 613 boys, 731 girls) to the control arm. Seventy-three schools (98.6%) were followed-up at 3-months (36 intervention (1,293 students); 37 control (1,243 students)). SFI reach was high (668/683, 97.8% Bangladesh; 605/610, 99.2% Pakistan). Most awareness-raising sessions were fully implemented in Bangladesh while implementation was more mixed (fully/partially implemented) in Pakistan. Fidelity to the pledge was 83.9% (594/708) in Bangladesh; 81.2% (568/699) in Pakistan. Completion of the certificate was (83.1% (588/708) in Bangladesh, 91.2% (638/699) in Pakistan. The primary outcome was children’s salivary cotinine, measured at baseline and three months after randomisation. We found that the mean cotinine concentration was -0.5% (95% Confidence Interval (CI): -19.9 to 23.7, p=0.965) lower in the SFI than control arm, translating to an estimated difference in marginal means of -0.004 ng/mL (95% CI -0.201 to 0.192). The adjusted incremental costs of SFI were purchasing power parity (PPP) US$58.89 (95% CI=PPP US$40.38 to PPP US$76.55) and the adjusted incremental Quality Adjusted Life Years (QALY) were 0.004 (95% CI= -0.001 to 0.009). These findings indicate that despite high reach and partial to full implementation, SFI was not effective or cost-effective in reducing exposure to SHS in primary school children in Bangladesh and Pakistan, and cannot therefore be recommended for use. Any efforts to reduce SHS exposure among children should be combined with the robust and comprehensive enforcement of smoke-free bans.