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. Subgroup analyses to assess for any association of patient characteristics with intervention responsiveness will be exploratory.