Influenza infection leads to significant morbidity and mortality each year. Influenza vaccines can reduce the risk of flu and the severity of flu illness, In addition, flu vaccinations can reduce flu complications such as pneumonia or worsening of chronic heart or lung disease. Each year, Kaiser Permanente of Colorado offers influenza vaccines to patients at no cost either at primary care clinic appointments or flu walk-in clinics in the fall prior to the upcoming flu season. In addition, as part of clinic appointment reminder text messages, there is a message to get the flu vaccine for patients who have not received the vaccine prior to the clinic visit. Building on these flu reminder text messages for patients who have not received a flu vaccine, this study will test different behavioral nudge text messages to improve influenza vaccination rates.

Inclusion Criteria:

• Patients 6 months and older who have not received a flu shot at the time of their primary care clinic appointment reminder will be eligible to receive a flu vaccine reminder text message. For children <18 years of age, their caregiver will receive the text message

Exclusion Criteria:

• Patients not eligible for flu vaccine