Patient Portal Flu Vaccine Reminders_RCT 5 (LADHS)

This trial is taking place in Los Angeles, CA at clinics within the Los Angeles Department of Health clinics. The study design is a comparative effectiveness trial design. Patients will be randomized into 1) receiving enhanced texting with a callback by a trained call-center staff member to schedule a vaccine visit if the patient presses "1" in response to the text, 2) receiving enhanced bidirectional texting with a texting response from a trained call-center staff member who will help the patient schedule a vaccine visit through a series of back-and-forth texts, or 3) standard text reminders (control group). Patients in all arms will receive reminders if they are due for influenza vaccine. Despite the Advisory Committee on Immunization Practices (ACIP) recommendation in 2010 that all people above 6 months of age should receive an annual flu vaccine, vaccination rates remain low: at 6m-4.9 yrs. (70%), 5-17.9 yrs. (56%), 18-64.9 yrs. (38%), and \>65 yrs. (63%). The investigators will assess the effectiveness of enhanced text R/R messages as compared to the standard of care control (standard text reminders).