Financial Incentives for COVID-19 Vaccination: A Cluster Randomized Clinical Trial

Area of Science:

• Public Health
• Health Economics
• Epidemiology

Background:

• Financial incentives are studied for increasing COVID-19 vaccination rates.
• Previous research indicates small positive direct effects but potential negative social spillovers.
• Unmeasured social spillovers may diminish the overall effectiveness of incentive policies.

Purpose of the Study:

• To assess the spillover effects of a COVID-19 vaccination financial incentive.
• To determine if spillover estimates impact broader evaluations of policy effectiveness.

Main Methods:

• Population-level, address-cluster randomized clinical trial in Ravensburg, Germany (November 2021).
• Adult residents randomly assigned to receive a €40 incentive for vaccination or a control letter.
• Intention-to-treat analysis of primary and booster COVID-19 vaccination uptake.

Main Results:

• No significant direct, spillover, or overall effects on primary COVID-19 vaccinations.
• Negative, statistically significant overall effect on booster vaccinations (-0.30 percentage points).
• Negative, statistically significant spillover effect on booster vaccinations (-0.29 percentage points) for initial vaccination events.

Conclusions:

• Direct effects of financial incentives on COVID-19 vaccination uptake were null.
• Negative spillover effects on booster uptake were observed among indirectly exposed individuals.
• Cohabitants may postpone booster vaccinations, potentially undermining incentive policy effectiveness.