In a large influenza-vaccination trial, reminders increased vaccination, while small cash and lottery incentives did not outperform the reminder alone.
Research question
Do lottery or cash incentives increase influenza vaccination beyond a reminder, and can targeting improve their cost-effectiveness?
Method & data
A randomized trial in an integrated health system compared no contact, a reminder, cash, and a lottery message; causal forests estimated heterogeneous treatment effects from health-record and area characteristics.
Main finding
All active outreach increased vaccination, but the incentive arms did not differ significantly from the reminder. Predicted responsiveness varied more for incentives than for reminders.
Why it matters
The study separates the value of outreach from the value of payment and shows where targeting methods may be useful.
What to verify
The public abstract covers one integrated health system and one influenza season; broader external validity is not stated.
Show public abstract used for this summary
Financial incentives may encourage vaccination, but their cost-effectiveness depends on targeting patients who are most responsive. We conducted a randomized controlled trial with 57,579 adult patients in an integrated health system during the 2021–2022 influenza season. Patients with an upcoming appointment were randomized to a no-contact control, a simple reminder, a $1 cash incentive, or a scratch-off lottery ticket incentive worth up to $5,000. Any active intervention increased vaccination at the scheduled appointment by 2 percentage points (an 8% increase over the control mean) and by 1.5 percentage points over the full influenza season. The three active arms did not differ significantly, indicating that small financial incentives provided no additional benefit beyond a reminder. Using electronic health records and area-level characteristics, we used causal forests to estimate conditional average treatment effects. Predicted responsiveness varied substantially: patients in the top quartile were 3–4 times more likely to respond to incentives than those in the bottom quartile, whereas reminder effects were relatively homogeneous. These findings suggest that low-cost reminders can increase influenza vaccination, while machine-learning methods can help identify patients most responsive to small financial incentives.