A small action that prompts the subject to alter or accelerate his or her behavior. And researchers at Wharton think they may have found a key to getting more people vaccinated.

In a new study, released February 18, the study’s authors found that certain text messages resulted in 11% higher vaccination rates. The study was conducted by the Behavior Change for Good Initiative at the Wharton School and the School of Arts and Sciences of the University of Pennsylvania, in collaboration with the Penn Medicine Nudge Unit. They partnered with Walmart and two regional health systems and sent 19 different messages to 50,000 patients ahead of planned visits to their primary care providers in the fall of 2020. The messages were designed to spur patients to get a flu vaccine.

What they found was eye-opening. Precisely how a message was worded had a huge impact on whether the patient ended up getting the shot. The top performing message? Two reminder texts sent 72 hours and 24 hours before the appointment. “The first message encouraged patients to request a flu shot at their upcoming appointment to protect the health of themselves and their families, and the second reminded patients that a flu shot had been reserved for their appointment. In this study, the most effective messages were unsurprising and lacked interactive components–they simply reminded patients that a flu shot was reserved for them at their doctor’s office. Messages that were more clever or informal, such as sharing a joke about the flu, were less effective,” the study’s authors wrote.

As my colleague Erika Fry has reported, so far vaccinations have been unevenly distributed by state. “Through Tuesday, Feb. 16, 12.2% of the U.S. population, or 40.3 million people, had received at least one dose of a COVID vaccine, up from 33.8 million a week ago according to data from the Centers for Disease Control. And 15.5 million individuals, or 4.7% of the population, have been fully vaccinated with two doses of either the Pfizer or Moderna vaccines. In total, the country has administered 56.3 million doses, or 77.8% of the 72.4 million distributed,” Fry wrote.

As vaccines become more widely available, however, these nudges could help with wider uptake, or conceivably with populations that have shown a reluctance to get vaccinated.

The researchers are optimistic that that what they’ve learned about the flu will help with COVID. “Our results suggest a promising way to encourage COVID-19 vaccinations at scale—we can potentially help save lives for less than 10¢ per person,” said Katy Milkman, Wharton professor, BCFG Co-Director, and lead author on the study. In the end, said Mitesh Patel, Penn Medicine Professor and PMNU Director, such seemingly small tweaks could “nudge vaccination rates higher and help us end this pandemic faster.”