Peers matter more: Age-based herding in COVID-19 vaccination

Herd behavior is a well-documented phenomenon in economics, yet little is known about whether people follow the general crowd or those who are most similar to them. This paper asks a simple but critical question: who do individuals really follow in a time of crisis? Using data from the European Social Survey combined with vaccination records across 15 countries, we examine how COVID-19 vaccination decisions were shaped by peers. We find that individuals’ willingness to vaccinate is driven far more strongly by their age-group peers than by the broader population, with the effect holding across most age groups. Moreover, our results reveal a U-shaped relationship between the share of vaccinated peers and individual vaccination intentions, suggesting that social norms reinforce peer effects once vaccination reaches a critical mass. These results highlight the perception that herd behavior is not just about the size of the herd; similarity is central to social learning and decision-making under uncertainty, with important implications for public health strategies and beyond. Regarding vaccination operations, these results indicate that mobilizing age-specific leaders, influencers, or social networks can help establish a herd within high-risk groups. More generally, as social learning appears to be most effective among individuals with shared characteristics, interventions designed to increase compliance may be more successful when targeted to specific peer groups rather than the general public.