The purpose of this study is to test which modalities (mailed letter, short message service [SMS] text, or patient portal messages) are most effective for encouraging flu shots in high-risk patients.

The Centers for Disease Control (CDC) recommends a flu vaccination to everyone aged 6+ months, with rare exception; almost anyone can benefit from the vaccine, which can reduce illnesses, missed work, hospitalizations, and death. Flu shots are particularly important for patients at high risk of experiencing severe outcomes.

During the 2020-21 and 2021-22 flu seasons, the study team sent messages to Geisinger patients in the top 10% of risk for flu and complications according to an artificial intelligence algorithm. Messages that told patients they were at high risk significantly increased their likelihood of getting vaccinated.

The present study will extend previous work by testing which modality or modalities are most effective at boosting flu shot rates in patients at high risk. In previous campaigns, patients received messages via all communication modalities patients were eligible for (mailed letter, SMS text, and/or patient portal message). In this study, patients will be randomized to receive high-risk messages in one or more modalities.

Inclusion Criteria:

• Included on a list of 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
• In the top 10% of risk for flu and flu complications, according to Medial's flu complications machine learning algorithm (which operates on coded EHR data)
• Has a Geisinger PCP assigned as of August 2022
• Has had an encounter in the last 2 years as of August 2022

Exclusion Criteria:

- Cannot be contacted via any of the communication modalities (e.g., letter, patient portal, SMS) being used in the study, either due to insufficient/missing contact information in the EHR or because they opted out of all modalities

Data with no personally identifiable information will be made available to other researchers on the Open Science Framework for transparency. This will include the essential data and code needed to replicate the analysis that yielded reported findings.

The data will become available after publication of study results in a scientific journal and will be available as long as the Open Science Framework hosts the data.

The data on the Open Science Framework will be open to anyone requesting that information.

Providers who prescribe vaccination and diagnose conditions will not be randomized to study arms or informed of patient assignment. Although patients will not be explicitly informed which arm they have been randomized to, they will be aware of the messages they receive.