The megastudy conducted by the authors aimed to evaluate the effectiveness of offering free round-trip Lyft rides to vaccination sites compared to sending behaviorally informed text message reminders for COVID-19 vaccinations. The study involved over 3.66 million CVS Pharmacy patients in the United States and tested seven different sets of behaviorally informed vaccine reminder messages. The results showed that providing free rides to vaccination sites did not significantly increase vaccination rates compared to sending text reminders. Specifically, the intervention of offering free Lyft rides did not produce measurable benefits over and above sending two text reminders that followed best practices from previous research. The study found that three types of personalized text reminders—encouraging patients to make a vaccination plan, communicating high infection rates in their county, and appearing to be sent directly by the pharmacy team—were the most effective in increasing vaccination rates. These reminders increased the 30-day COVID-19 booster uptake by 21% and also had a spillover effect, increasing 30-day influenza vaccinations by 8%. The findings suggest that behaviorally informed text message reminders are a cost-effective way to increase vaccination rates, while free rides to vaccination sites may not be as beneficial. The study also highlighted the need for more rigorous testing of interventions to promote vaccination and the importance of accurate forecasting to ensure that evidence-based solutions are widely adopted.The megastudy conducted by the authors aimed to evaluate the effectiveness of offering free round-trip Lyft rides to vaccination sites compared to sending behaviorally informed text message reminders for COVID-19 vaccinations. The study involved over 3.66 million CVS Pharmacy patients in the United States and tested seven different sets of behaviorally informed vaccine reminder messages. The results showed that providing free rides to vaccination sites did not significantly increase vaccination rates compared to sending text reminders. Specifically, the intervention of offering free Lyft rides did not produce measurable benefits over and above sending two text reminders that followed best practices from previous research. The study found that three types of personalized text reminders—encouraging patients to make a vaccination plan, communicating high infection rates in their county, and appearing to be sent directly by the pharmacy team—were the most effective in increasing vaccination rates. These reminders increased the 30-day COVID-19 booster uptake by 21% and also had a spillover effect, increasing 30-day influenza vaccinations by 8%. The findings suggest that behaviorally informed text message reminders are a cost-effective way to increase vaccination rates, while free rides to vaccination sites may not be as beneficial. The study also highlighted the need for more rigorous testing of interventions to promote vaccination and the importance of accurate forecasting to ensure that evidence-based solutions are widely adopted.