Nudging Flu Vaccination by Making it Easy for Patients to Schedule a Flu Shot

Inclusion Criteria: * Included in one or both of the following two base patient lists: 1. Geisinger patient portal flu outreach list for Fall 2022 2. A list of patients obtained from Geisinger's Phenomics and Clinical Data Core (PACDC). This list will include active Geisinger patients (all patients on this list attended at least one primary care appointment at Geisinger between 10/1/2008 and 4/13/2022, and either had a Geisinger primary care provider assigned as of April 2022, or were in the Electronic Health Record \[EHR\] since at least September 2021 and had at least one encounter in 2020-2022). * Aged 18 or older as of October 2022 * Has had a Geisinger encounter in the last 2 years as of October 2022 * Either of the following, as of October 2022: 1. Has a Geisinger PCP assigned in the Community Medicine, Pediatrics, or Internal Medicine service line 2. In the last 2 years, has completed an appointment in a Geisinger specialty on a list of specialties approved by system leadership for flu shot communications * Has not received a flu-shot during the 2022-23 flu season as of \~1 week prior to the message date (timeline may be slightly different, depending on data pull logistics), according to the Electronic Health Record (EHR) * Does not have a scheduled in-person primary care or in-person flu-shot-eligible specialty appointment in the 12 weeks following their assigned message send date, as of \~1 week prior to the message date (timelines may be slightly different, depending on data pull logistics or clinical guidance) * As of this writing, the team plans to define a flu-shot-eligible specialty appointments as appointments in departments that have historically documented or administered flu vaccine. However, this approach may change slightly based on changing clinical guidance. Exclusion Criteria: * The CMSL/Marketing list will include patients in Geisinger's 65Forward or Community Care populations. If necessary due to logistical constraints, we may exclude these 65Forward and/or Community Care patients from our study. * Cannot be contacted via the communication modality being used in the study (e.g., patient portal, SMS), e.g., due to insufficient/missing contact information in the EHR or because they opted out * Has an allergy to flu vaccines according to any EHR allergy table known to the study team * Has a health maintenance modifier indicating they are permanently discontinued from receiving a seasonal flu shot * Is on a list of dismissed patients