Cardiovascular-Focused Messaging to Improve Influenza Vaccination Rates.

Background: Influenza vaccination rates remain suboptimal despite strong evidence of benefit. Electronic letters emphasizing the cardiovascular benefits of vaccination increased uptake in Denmark; whether this strategy is effective in a diverse U.S. population is unknown.

Methods: In this prospective, randomized, open, blinded end point trial involving a multiregional health care system, adults were randomly assigned 1:1:1:1 to receive cardiovascular-focused messaging versus usual care messaging to encourage influenza vaccination at two trial time points, yielding four groups, with each in receipt of either two rounds of cardiovascular-focused nudges; a cardiovascular-focused nudge followed by usual care communication; usual care communication followed by a cardiovascular-focused nudge; or two rounds of usual care communication. The primary end point was influenza vaccination receipt through January 1, 2025. Outcomes were assessed across six coprimary comparisons.

Results: Overall, 3,668,428 adults were randomly assigned across three U.S. states and Washington, DC. Participants had a mean (±SD) age of 48.36 (±18.11) years, 52.87% (n=1,939,352) were women, 10.53% (n=386,393) were Black, and 702,493 (19.15%) had cardiovascular disease. Overall vaccination rate at the end of the trial was 32.46%. Compared with participants who received two rounds of usual care communication, those receiving cardiovascular-focused messaging at any time point had similar vaccination rates (32.41% vs. 32.60%; absolute change, -0.19 percentage points; 99.2% confidence interval, -0.34 to -0.04). Time to vaccination did not differ.

Conclusions: In a large individually randomized trial embedded in routine care across a national U.S. health system, a cardiovascular-focused nudge intervention did not increase influenza vaccination rates on a background of low uptake. Nevertheless, this trial illustrates the feasibility of conducting large care-embedded trials of nudges in U.S. health systems. (Funded by Kaiser Permanente's Garfield Memorial Fund; trial registration, ClinicalTrials.gov NCT06571747.).