The proposed RCT evaluates the efficacy of the aforementioned novel 2-month online smoking cessation intervention in increasing 7-day point prevalence quit rate over a 6-month follow-up period among Chinese adult smokers in Hong Kong.

Aims and hypothesis: The proposed RCT evaluates the efficacy of the aforementioned novel 2-month online smoking cessation intervention in increasing 7-day point prevalence quit rate over a 6-month follow-up period among Chinese adult smokers in Hong Kong. It is hypothesized that the quit rate of the intervention group would be higher than that of the control group at 6 month follow up (i.e. one-sided hypothesis).

Design and subjects: The RCT study will randomize participants into the intervention group or the control group. Prior to randomization, a baseline telephone survey will be conducted. Phone interviews will be conducted to evaluate the outcomes at Months 3 and 6 after completion of the intervention. Interviewers will be blinded from the randomization status. The inclusion criteria are: i) current smokers who have smoked at least one cigarette in the past seven days prior to the baseline survey, ii) age 18 years old or above, iii) able to communicate in Chinese (Cantonese), iv) having access to a smart phone or mobile electronic devices and social networking media (WeChat), v) willing to be followed up (Months 3 and 6), vi) should own a smart phone or a similar device.

Study instruments: Structured questionnaires.

Interventions: The 2-month intervention includes i) interactive online support groups and ii) immediate preventive 'SOS' cue to action messages to be sent to fellow support group members in need via WeChat. Besides, basic health education messages will be sent to both the intervention and the control groups.

Main outcome measures: self-reported 7-day point prevalence (pp) quit rate of smokers at 6 months post end-of-intervention.

Data analysis and expected results: Baseline characteristics between the two groups will be compared using t-test and chi-square test as appropriate. To evaluate efficacy in terms of the primary outcome, absolute risk reduction (ARR), relative risk reduction (RRR) and number needed to treat (NNT) at Months 3 and 6 and their 95% confidence intervals will be derived. Mixed effects models will be used to compare the differential changes on the outcome variables across the time points Months 0, 3 and 6 between the two study arms with adjustment for potential confounding variables. Significance differences in smoking cessation will be found among the two groups.

Inclusion Criteria:

• Current smokers who have smoked at least one cigarette in the past seven days prior to the baseline survey
• Age 18 years old or above
• Able to communicate in Chinese (Cantonese)
• Having access to a smart phone or mobile electronic devices and social networking media (WeChat), v) willing to be followed up (Months 3 and 6)
• Should own a smart phone or a similar device

Exclusion Criteria:

• Physically or mentally unfit
• Having participated in smoking cessation programs (last six months)