To evaluate the relative efficacy of an online intervention based on the Trans-theoretical Model delivered by a fully-automated Chatbot with natural language processing functions versus a control in promoting pneumococcal vaccination uptake among Hong Kong people aged ≥65 years. A total of 374 participants will be randomized evenly to either the intervention group or the control group. Participants in the intervention group will receive Chatbot-delivered interventions tailored to their stage of change regarding PV uptake in a conversational way at Month 0, 1, 2, and 3. Participants in the control group will receive Chatbot-delivered general information related to PV at Month 0, 1, 2, and 3. All participants will be followed up 6 and 12 months after completion of the intervention.

Inclusion Criteria:

• aged ≥65 years
• having Hong Kong ID
• Chinese speaking
• have not received any penumococcal vaccination
• willing to be followed up by telephone
• having a smartphone
• able to send and read text/voice messages via smartphone.

Exclusion Criteria:

• blindness or deafness
• not able to communicate with others effectively
• with known contradictions of pneumococcal vaccination
• having been diagnosed with major psychiatric illness
• scored ≤16 in the validated telephone version of the Cantonese Mini-mental State Examination (T-CMMSE).