Sequential Digital Intervention to Increase Influenza Vaccination in Patients With Heart Failure

Influenza vaccination is an important preventive measure for patients with heart failure (HF), but vaccination uptake remains low in China. Although previous studies have demonstrated the benefits of actively promoting influenza vaccination, scalable strategies to improve vaccination uptake among patients with HF after hospital discharge remain insufficiently evaluated. The PANDA-BOOST trial is a prospective, pragmatic, open-label, two-stage sequential randomized clinical trial involving participants previously enrolled in the PANDA II trial. The study aims to evaluate whether sequential digital interventions using artificial intelligence (AI)-assisted telephone calls and short message service (SMS) reminders improve influenza vaccination uptake compared with a single routine vaccination recommendation. After an initial AI-assisted telephone call providing a standardized influenza vaccination recommendation, eligible unvaccinated participants will be randomized in a 1:2 ratio to a routine recommendation group or a sequential digital intervention group. Participants in the sequential intervention group will receive additional AI-assisted telephone calls approximately 14 and 28 days after the initial call. Those who remain unvaccinated and meet eligibility criteria at the third call will undergo a second randomization in a 1:1:1 ratio to no additional SMS, gain-framed SMS, or loss-framed SMS. The primary outcome is influenza vaccination uptake within two months after the first-stage randomization.

Inclusion Criteria: 1. Previous participation in the PANDA II randomized clinical trial. 2. Confirmed to be alive at the initial artificial intelligence (AI)-assisted telephone assessment. 3. Successful telephone contact with sufficient information to determine current-season influenza vaccination status. 4. Not having received the 2026-2027 seasonal influenza vaccine at the time of the initial telephone assessment. Exclusion Criteria: 1. Receipt of the 2026-2027 seasonal influenza vaccine before or at the initial telephone assessment. 2. Unable to establish effective telephone contact after prespecified contact attempts. 3. Unable to ascertain current-season influenza vaccination status during the initial telephone assessment. Eligibility for Second-Stage Randomization: Among participants assigned to the sequential digital intervention group, those who complete the third AI-assisted telephone assessment and remain unvaccinated against seasonal influenza will be eligible for second-stage randomization. Participants who have been vaccinated, cannot be successfully contacted, or have an undetermined vaccination status at the third assessment will not undergo second-stage randomization.