Governments around the world are still trying to figure out how to convince people to get vaccinations and booster shots against covid-19. A large new study suggests a well-phrased text message or two could help move the needle.
The study of 689,693 Walmart pharmacy customers, published in the journal PNAS, explored whether behavioral nudges (in this case, text messages) might encourage people to get their flu shots during the fall and winter of 2020. Indeed, reminder texts boosted vaccination rates among Walmart pharmacy customers by 7%, or two percentage points, compared to a control group who did not receive text messages.
While the study focused on flu vaccines rather than covid vaccines, the study’s authors created the experiment with covid in mind, and used text messages that would also be applicable for covid vaccines as they became available.
“We felt like the flu was a really good proxy, in that it’s a vaccine that only half of Americans take, and at the time when we were starting our project, about half of Americans were saying they were definitely going to get [covid] vaccines and the other half weren’t sure yet,” says Katy Milkman, a professor at the University of Pennsylvania, and one of the study’s authors.
Another study, conducted when covid vaccines first became widely available in 2021, also found that text reminders increased covid vaccination rates by 26%, or four percentage points.
Milkman doesn’t claim that texts will overcome vaccine hesitancy. “These messages were designed to get people to take action who are not super highly motivated,” she says. In other words, a nudge from a healthcare provider isn’t likely to make a big difference for people who are actively opposed to taking the vaccine. But it may be quite helpful for someone who’s just dragging their feet.
The most effective language for vaccine reminders
Of the 22 text messages included in the study, the most effective reminder boosted vaccinations by 10% (three percentage points) compared to the control group. It consisted of two parts.
First, “It’s flu season & you can get a flu shot at Walmart.” Seventy-two hours later, “A flu shot is waiting for you at Walmart.” The second-most-effective nudge also included multiple texts and said that a shot was waiting for customers.
“Nagging someone, it works—up to a point,” says Milkman.
The results also demonstrate the power of what Milkman calls “ownership language”: Texts that say a shot is “waiting for you” or “reserved for you.” Research by economist Richard Thaler, among others, shows that we value things more when we feel that they belong to us.
This kind of language can also make people feel as if they’re getting insider access, according to research by Jon Bogard, another co-author of the PNAS study and a PhD student at the University of California Los Angeles. “Whether it’s a vaccine or a concert, they’re excited about the opportunity that’s exclusive to them, and they want to seize the day,” says Milkman.
Nudging people toward booster shots
The Walmart customers in the study were all people who had received a flu shot the previous year. “It’s very comparable to people who’ve gotten a first dose but not a second dose [of a covid vaccine], or a second dose but not a booster,” says Milkman.
In the US, while 87% of people over age 18 have received at least one vaccine dose, 74% have received two doses, and just 45% have gotten their booster shots, according to data from the Centers for Disease Control. And given the possibility that annual covid booster shots may be necessary, Milkman says that identifying small, inexpensive ways to incentivize people to get their jabs will remain important.
This post has been updated.