Problem: Influenza and pneumonia is the #8 leading cause of death among children. The influenza vaccine is on the recommended schedule for children and is effective against severe disease. However, families may have different reasons they chose to vaccinate or not vaccinate their child against influenza. Caregivers may want more information about whether their child is at risk for influenza overall or for severe disease and may have doubts regarding vaccine effectiveness and/or vaccine safety. They may also not know when and where they can get the vaccine or what the best time is to be vaccinated for optimal protection, should they decide they want their child to be vaccinated. Pediatricians want families to have the information they would find most helpful to them. Vaccine text messages are widely recommended. Families are busy and often have multiple competing obligations and want information given to them in way that is accessible. Text messaging, as a single-method communication, is a low-cost, scalable, and easy way to provide families with information to help support them to make a vaccine decision they feel is best for their child. If a family does want to be vaccinated, text messages can also help to provide information on when, where and how to get vaccinated. Should they decide not to vaccinate, they can also be well-informed in that decision. We propose a pragmatic implementation study with national scope vital to understanding how best to use influenza text message reminders in a way that is meaningful to parents. AIM 1. To assess the use of influenza vaccine text messages to provide health-related information that parents find informative in deciding whether or not to vaccinate their child against influenza. AIM 2. To assess parental and child characteristics that affect parent engagement with informational influenza vaccine text messages in order to optimize messages for all families AIM 3. To identify contextual factors, facilitators and barriers to implementation and sustainability of health-related text messages for families. Methods: This multi-site trial will include 60,000 parents of 6 month-17-year-old children who are due for the influenza vaccine. Practices will be recruited through a national primary care network. Randomization will occur at the individual level 1:1:1:1 stratified by site, age group, and prior year’s vaccine history: three arms will include different types of educational messages and one arm will be no messages (usual care). Messages will be sent centrally and managed by the research team. Building on results of season 1, we will augment messages based on needs identified and work with families to update messages to best meet their informational needs. We will then conduct a large scale implementation study of the optimized messages in which practices will implement the health-related text messages on their own, should they decide to. Using a mixed-methods approach, we will use the RE-AIM framework in comb...