Use of Construal Level Theory to Inform Messaging to Increase Vaccination Against COVID-19

This study aims to increase uptake of the COVID booster vaccine through messaging informed by Construal Level Theory. Patients in the Mass General Brigham (MGB) health system aged 18 and older who are eligible for the COVID booster vaccine, but who have not yet received a dose at the time of an upcoming primary care clinic visit, will be randomized to one of three messaging arms: 1) "why" messaging, 2) "how" messaging, or 3) standard of care ("usual care"). Messages will be sent via the electronic patient portal a few days in advance of their office visit. The primary outcome will be the rate of booster vaccination at the targeted visit. The secondary outcome will be the rate of receipt of a COVID booster vaccine within 6 weeks of the targeted visit.

In this arm, patients will be sent an electronic patient portal message a few days in advance of their office visit. Messages will focus on reasons to get the COVID booster vaccine, including protecting self and loved ones or the idea of herd immunity.

In this arm, patients will be sent an electronic patient portal message a few days in advance of their office visit. "How" messages will focus on the details of obtaining a vaccination at MGB, what to expect, and how to prepare for the visit.

In this arm, patients will not receive any additional message about their upcoming visit, beyond what they already receive by the health system.

Messages are informed by construal level theory, which suggests that emphasizing "why" elicits more abstract thinking, or high-level construals, and can induce an emotional mindset, which could challenge an individual's sense of identity, autonomy, or political preferences. Conversely, emphasizing "how" is more cognitive and evokes concrete thinking, or low-level construals, and encourages a planning or implementation mindset, which may be better for encouraging vaccine uptake.

Inclusion Criteria: Patients in the Mass General Brigham system Aged 18 and older Are eligible for the COVID booster vaccine but have not received a dose at time of upcoming primary care clinic visit Exclusion Criteria: Documented allergy to a COVID vaccine or its components Home address outside of Massachusetts Did not receive full set of primary COVID-19 vaccination series