Table 2.
Characteristics and key findings of included studies.
| Citation | Study Design | Participants and Study Period | Intervention Type | Comparator | Outcome Variable | Key Findings | Risk of Bias |
|---|---|---|---|---|---|---|---|
| Chan et al., 2022 [36] | Non-randomized uncontrolled before–after study | Healthcare employees (n = 13,942) living in Oregon and Washington state, USA (August–October 2021) | Complex intervention with multiple components (including town halls, meetings, optional vaccine counselling, etc.) | Before–after comparison | Rate of complete vaccination among participants (immunization records obtained via state CDC Immunization Information Systems and reconciled with EMR employee data) | 9.8% absolute increase in complete vaccination rate after intervention | Moderate |
| Crutcher & Seidler, 2021 [35] | Non-randomized controlled cluster trial | Adults and children >12 years (number of participants not reported) living in Los Angeles, California, USA (June–July 2021) | Educational infographic | Control group (county-wide) comparison and before–after comparison | Completion of second vaccine dose for COVID-19 (determined from Lincoln Park vaccination site records) | The Lincoln Park vaccination site served 15.8% more second-dose recipients when compared to all of Los Angeles County vaccine sites in the same timeframe | Moderate |
| Dai et al., 2021 [37] | 2 sequential randomized controlled trials | Adult patients (n = 93,354 for first trial, n = 67,092 for second trial) from the UCLA Health patient list in Los Angeles, California, USA (January–May 2021) | Text-based reminders with or without video | Control group (for both trials) | Vaccination rates (immunization records available through the UCLA healthcare system) | The first reminder (first trial intervention) resulted in a 3.57% absolute increase in vaccine uptake, and the second reminder (second trial intervention) resulted in a 1.06% absolute increase. | Low |
| Lieu et al., 2022 [38] | Randomized controlled trial | Latino and Black adults (n = 8287) living in Northern California, USA (March–May 2021) | Culturally tailored outreach via letters and secure electronic messaging | Control group (usual care) | Completion of at least 1 dose of a COVID-19 vaccine (according to state immunization records) | Patients receiving both standard (adjusted HR: 1.17; 95% CI, 1.04–1.31) and culturally tailored (aHR: 1.22; 95% CI, 1.09–1.37) outreach demonstrated higher vaccination rates compared to usual care | Some concerns |
| Mehta et al., 2022 [39] | Randomized controlled trial | Adults (n = 16,045) living in Philadelphia, Pennsylvania, USA (April–July 2021) | Text message, with standard, scarcity, clinical endorsement, and endowment message framing | Control group (received standard telephone call) | Proportion of patients who completed the first dose of the COVID-19 vaccine within 1 month of intervention (according to EMR) | No detectable increase in vaccine uptake among patients receiving text messages or behaviourally informed message content compared to telephone calls only | Low |
| Tentori et al., 2022 [40] | Randomized controlled trial | Adults (n = 2000) living in Trento Province, Italy (July–August 2021) | Vaccine appointment booking, with option to ‘opt-out’ | Control group (received usual ‘opt-in’ option to schedule vaccination appointment) | Vaccination rate (obtained from provincial records) | 32% relative increase in vaccination rate among those in ‘opt-out’ group when compared to the ‘opt-in’ (control) group | Low |