Over the next couple of months, other countries will probably surpass the U.S. on rates of COVID-19 vaccination. The reason is not lack of supply, but vaccine hesitancy. How can more Americans be persuaded to get their shots? Insights from behavioral economics can help.

The U.S. as a whole is approaching having 40% of the population fully vaccinated, but the proportion varies widely from state to state. Almost half of people in Maine have had their shots, but only about 30% in Georgia, Tennessee, Louisiana and Wyoming.

About a quarter of Americans say they don’t want to get vaccinated. That share has declined slightly over the past six months, but it’s higher than in most other countries. In almost every developed economy except France, the share of people who would get vaccinated if offered the chance is 10 to 20 percentage points higher than in the U.S. So as vaccines become increasingly available worldwide, the vaccination rate in the U.S. stands to lag.