This experiment is part of a megastudy with a total of ten experimental conditions and a holdout control condition to which patients will be randomly assigned. The focal comparison in this experiment is between a message suggesting the same day of the week, at the same time of day, and at the same pharmacy location as their last vaccination and a control message telling patients that an updated COVID booster vaccine is waiting for them. The intervention testing if text messages encouraging vaccination by suggesting patients receive a shot on the same day of the week, at the same time of day, and at the same pharmacy location as their last vaccination will produce more vaccinations than otherwise identical messages.

Exclusion Criteria:

1. The patient unsubscribed from texts before the send date and time of the patient's SMS/MMS message
2. The patient received a bivalent COVID booster before the send date and time of the patient's SMS/MMS message.

As treated participants will receive text messages, there is no scope for blinding. Care providers will not be made aware of subjects' participation in the study, or assigned treatment arms. The study team will only receive data on subjects' assigned arms and outcomes at the end of the study.