RANDOMIZED CONTROLLED TRIAL OF TEXT MESSAGE TO INCREASE PNEUMOCOCCAL VACCINATION IN ADULTS IN CHILE.

The goal of this randomized controlled trial is to learn if text message reminders sent through WhatsApp increase pneumococcal vaccination coverage in adults turning 65 years old in Chile. The main questions it aims to answer are: Do text message reminders increase the proportion of adults aged 65 years who receive the pneumococcal vaccine compared to usual care? Do text message reminders increase pneumococcal vaccination coverage within the first 7 days after the message is sent? Is there an association between socioeconomic factors and pneumococcal vaccination coverage in adults aged 65 years in Chile? Researchers will compare adults who receive a text message reminder to adults who receive no reminder (usual care) to see if the reminders increase vaccination uptake. Participants will: Be randomly assigned to receive a WhatsApp text message reminder about the pneumococcal vaccine or to receive no reminder Receive a second reminder on day 14 if they have not yet been vaccinated (intervention group only) Be followed for 6 weeks, with vaccination status checked at days 7, 21, and 42 from the start of the intervention

Inclusion Criteria: * Adults born during the year 1961, turning 65 years of age in 2026 * Resident in Chile at the time of the study * Valid mobile phone number registered in the National Immunization Registry (RNI) Exclusion Criteria: * Record of pneumococcal vaccination in the National Immunization Registry (RNI). * Identified as deceased in the Chilean Civil Registry and Identification Service.