Communication Intervention to Improve Influenza Vaccination Rates Among Elderly in Can Tho

This study employs a cluster randomised controlled trial (cluster RCT) design with a repeated cross-sectional approach. The unit of randomisation is the cluster (ward or commune).

RANDOMISATION:

From eight study sites surveyed in Objective 1 (four urban wards and four rural communes in Can Tho City), four sites were selected by stratified lottery randomisation. Within each stratum (urban and rural), one site was randomly assigned to the intervention group and one to the control group by lottery draw without investigator discretion:

• Intervention: O Mon Ward (urban) and Truong Thanh Commune (rural)
• Control: Phuoc Thoi Ward (urban) and Truong Xuan Commune (rural)

PARTICIPANTS:

All eligible permanent residents aged above 65 years at each study site were invited to participate. Data are collected at two independent cross-sectional time points:

• T0: Baseline survey, August 2025 (n=952)
• T1: Follow-up survey, September 2026 (n=approximately 1,200) Participants at T0 and T1 are not necessarily the same individuals; the design captures population-level changes within randomised clusters.

INTERVENTION (12 months: September 2025 to September 2026):

The 12-month duration encompasses both active implementation and the time required for knowledge, attitude, and behaviour change.

Phase 1 (September 2025, intensive activities):

• Two community health education sessions per intervention site for adults aged >65 years and one cohabiting family member, with distribution of printed educational leaflets on influenza disease and vaccination. Attendance: O Mon Ward: Session 1 = 60 older adults + 40 family members, Session 2 = 57 older adults + 35 family members; Truong Thanh Commune: Session 1 = 60 + 38, Session 2 = 50 + 30.
• One capacity-building workshop per site for healthcare workers and community health volunteers in vaccination counselling (O Mon Ward: n=30; Truong Thanh Commune: n=20).
• Thirty household visits per site by trained community health volunteers to reinforce vaccination counselling.

Phase 2 (September 2025 to September 2026, ongoing):

• Health communication banners displayed at health stations and community information centres throughout the intervention period.
• Healthcare worker vaccination counselling integrated into all routine clinical contacts at intervention site health stations.
• Zalo-based digital communication: weekly educational content and personalised vaccination reminders (December 2025 to January 2026, coinciding with peak influenza season in southern Vietnam).

CONTROL GROUP:

Received routine primary healthcare only, with no additional study-related activities.

ANALYSIS:

Effectiveness is measured using Difference-in-Differences (DID) regression, comparing changes between T0 and T1 across intervention and control clusters. Models use multivariable logistic regression (binary outcomes) and linear regression (continuous outcomes), adjusted for sociodemographic covariates. Intraclass correlation coefficients (ICC) were estimated for all outcomes and found to be negligible (ICC < 0.01), confirming the appropriateness of individual-level DID analysis.

Inclusion criteria

• Residents living in selected wards/communes in Can Tho City for at least 6 months.
• Aged above 65 years.
• Mentally and physically capable of participating in interviews and receiving communication interventions.
• Agree to participate in the study and provide informed consent.

Exclusion criteria

• Individuals with severe cognitive impairment or dementia.
• Individuals with contraindications to influenza vaccination.
• Planning to move out of the study area during the 12-month follow-up period.