A 680,000-person megastudy of nudges to encourage vaccination in pharmacies

Katherine L. Milkman*, Linnea Gandhi, Mitesh S. Patel, Heather N. Graci, Dena M. Gromet, Hung Ho, Joseph S. Kay, Timothy W. Lee, Jake Rothschild, Jonathan E. Bogard, Ilana Brody, Christopher F. Chabris, Edward Chang, Gretchen B. Chapman, Jennifer E. Dannals, Noah J. Goldstein, Amir Goren, Hal Hershfield, Alex Hirsch, Jillian HmurovicSamantha Horn, Dean S. Karlan, Ariella S. Kristal, Cait Lamberton, Michelle N. Meyer, Allison H. Oakes, Maurice E. Schweitzer, Maheen Shermohammed, Joachim Talloen, Caleb Warren, Ashley Whillans, Kuldeep N. Yadav, Julian J. Zlatev, Ron Berman, Chalanda N. Evans, Rahul Ladhania, Jens Ludwig, Nina Mazar, Sendhil Mullainathan, Christopher K. Snider, Jann Spiess, Eli Tsukayama, Lyle Ungar, Christophe Van den Bulte, Kevin G. Volpp, Angela L. Duckworth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

56 Scopus citations


Encouraging vaccination is a pressing policy problem. To assess whether text-based reminders can encourage pharmacy vaccination and what kinds of messages work best, we conducted a megastudy. We randomly assigned 689,693 Walmart pharmacy patients to receive one of 22 different text reminders using a variety of different behavioral science principles to nudge flu vaccination or to a business-as-usual control condition that received no messages. We found that the reminder texts that we tested increased pharmacy vaccination rates by an average of 2.0 percentage points, or 6.8%, over a 3-mo follow-up period. The mosteffective messages reminded patients that a flu shot was waiting for them and delivered reminders on multiple days. The topperforming intervention included two texts delivered 3 d apart and communicated to patients that a vaccine was "waiting for you." Neither experts nor lay people anticipated that this would be the best-performing treatment, underscoring the value of simultaneously testing many different nudges in a highly powered megastudy.

Original languageEnglish (US)
Article numbere2115126119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - Feb 8 2022


  • COVID-19
  • Field experiment
  • Influenza
  • Nudge
  • Vaccination

ASJC Scopus subject areas

  • General


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