Cardiovascular-Focused Messaging to Improve Influenza Vaccination Rates

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.

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.

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.

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.).