INTRODUCTION: About 5%-15% of the population of the United States contracts influenza annually, resulting in more than 20,000 deaths and significant economic impact. For people with cardiovascular disease (CVD), influenza can be particularly dangerous. In 1 study, the risk of heart attack was 6 times higher within a week of influenza infection. A study of more than 80,000 US adults hospitalized with influenza over 8 seasons found that 1 of every 8 patients developed sudden, serious cardiac complications, and that having underlying cardiac disease was significantly associated with experiencing an acute cardiac event with influenza. For these reasons, the Centers for Disease Control and Prevention (CDC) consider persons with CVD to be at high risk for influenza complications and therefore a priority group for vaccination.

Vaccination remains the most effective primary prevention method against influenza, with age-adjusted effectiveness rates of up to 68% over the past 5 years. The CDC reports a 51.4% vaccination rate for 2019-2020 for persons aged 18-64 years who have high-risk conditions such as CVD, far below the 70% national vaccination rate goal. Given the increased burden of influenza for people with CVD, even small improvements in vaccination rates could substantially reduce the number of patients having major adverse cardiac events.

Novel, scalable, cost-optimal, and effective solutions are needed to address barriers to influenza vaccination among people with CVD, such as complacency, time/cost constraints, and lack of confidence. Observational and randomized controlled trials have shown the effectiveness of digital messaging to increase vaccine uptake in general adult populations. In a randomized trial of digital messaging in persons with diabetes, a population also at increased risk of influenza-related complications, the vaccination rate was 3.1% higher in the intervention group compared with controls. Put another way, 33 people would need intervention to gain 1 additional vaccination.

The primary objective of this study was to examine the efficacy of a digital intervention designed to increase self-reported influenza vaccination rates in individuals with CVD.

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