A three-arm cluster randomized clinical trial examining tailored messaging interventions for updated COVID-19 vaccines in emergency departments (EDs) showed that neither messaging nor simple inquiry about vaccine acceptance significantly increased 30-day vaccine uptake compared with usual care, although vaccine availability emerged as an important modifier of intervention effectiveness.
Investigators enrolled 852 adult ED patients across six sites in San Francisco, Philadelphia, Houston, and Durham, North Carolina, from January 29 to June 18, 2024. Participants had not received a COVID-19 vaccine in the prior 6 months. The median age was 47 years (interquartile range, 33-63 years), and 464 (54.5%) were women. The study assigned 247 participants (29.0%) to intervention M (tailored messaging and vaccine acceptance inquiry), 273 (32.0%) to intervention Q (inquiry only), and 332 (39.0%) to usual care (control).
The primary outcome—updated COVID-19 vaccine receipt within 30 days—showed no significant difference between intervention M and control (14 participants [5.7%] vs 10 [3.0%]; absolute difference, 2.7 percentage points [pp]; 95% CI, −0.8 to 6.3). Similarly, intervention Q showed no significant increase versus control (11 [4.0%] vs 10 [3.0%]; absolute difference, 1.0 pp; 95% CI, −2.0 to 4.2).
However, at the three sites where updated vaccines were available in hospital pharmacies, intervention M demonstrated higher 30-day uptake compared with usual care (13 of 132 [9.8%] vs 5 of 150 [3.3%]; absolute difference, 6.5 pp; 95% CI, 0.5-12.5) and greater ED vaccination rates (8 of 132 [6.1%] vs 0 of 150; absolute difference, 6.1 pp; 95% CI, 1.6-10.5). Intervention Q also showed an increased ED vaccination rate versus control at sites with vaccine availability (7 of 130 [5.4%] vs 0 of 150; absolute difference, 5.4 pp; 95% CI, 1.1-9.7 ).
Among the 520 participants who received vaccine acceptance questions across both intervention groups, 163 (31.3%) initially accepted the vaccine, and 129 (24.8%) indicated they would still accept the vaccine after learning about potential costs (absolute difference, 6.5 pp; 95% CI, 4.7-9.0).
“The slight increase in uptake among participants in the EDs that had access to the updated COVID-19 vaccines suggested that vaccine availability was an effect modifier, underscoring the importance of opportunity and convenience in vaccine delivery,” the investigators stated.