Effect of Messaging on Pragmatic Outcomes Within an Integrated Healthcare System

Inclusion Criteria: * Aged ≥18 years; * Active KPSC member; * Continuous membership from 27 August 2025 to 28 September 2026; * Members who are aged 65 years and older, or adults aged 18-64 years with at least one of the following health conditions that increases their risk for severe COVID-19 illness, including: a) asthma, b) cancer, c) ischemic stroke, d) intracerebral or subarachnoid hemorrhage, e) transient ischemic attack, f) chronic kidney disease, g) dialysis, h) bronchiectasis, i) chronic obstructive, pulmonary disease (COPD), j) pulmonary fibrosis, k) cystic fibrosis, l) pulmonary hypertension, m) cirrhosis, n) non-alcoholic fatty liver disease (NALD), o) alcoholic liver disease, p) autoimmune hepatitis, q) diabetes, r) heart failure, s) coronary artery disease, t) cardiomyopathy, u) HIV, v) obesity, w) essential hypertension, x) primary immunodeficiency and other underlying immunocompromising conditions, y) solid organ or blood stem cell transplant, z) tuberculosis; * No documented receipt of updated 2026-27 COVID-19 vaccine as of 28 September 2026; * Has valid email information. Exclusion Criteria: * Unable to receive or opted out of email communication. * People with unknown or missing sex. * People who cannot safely receive a COVID-19 vaccine, including those who had a severe allergic reaction to a previous COVID-19 vaccine or have a contraindication to COVID-19 vaccine or a vaccine ingredient, will not be included in the study. * People with metastatic or terminal illness, advanced illness, receiving hospice or palliative care, or resident in skilled nursing facilities. * People who are pregnant or currently breastfeeding.