Effects of Side-Effect Risk Framing Strategies on COVID-19 Vaccine Intentions: A Randomized Controlled Trial

Fear over side-effects is one of the main drivers of COVID-19 vaccine hesitancy. We conducted a pre-registered randomized controlled trial among 8998 individuals to examine the effects of different ways of framing and presenting vaccine side-effects on individuals’ willingness to get vaccinated. We found that adding a descriptive risk label (“very low risk”) next to the numerical side-effect and providing a comparison to motor vehicle mortality increased participants’ willingness to take the COVID-19 vaccine by 3.0 percentage points (p = 0.003) and 2.4 percentage points (p = 0.049), respectively. These effects were independent and additive and combining both framing strategies increased willingness to receive the vaccine by 6.1 percentage points (p < 0.001). Mechanistically, we find evidence that these framing effects operate by increasing individuals’ perceptions of how safe the vaccine is. Our results reveal that low-cost side-effect framing strategies can meaningfully affect vaccine intentions at a population level.