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This week the COVID-19 vaccine developed by Pfizer and BioNTech was, at last, fully approved by the FDA for everyone aged 16 and older. The acting FDA commissioner, Janet Woodcock, described the move as a milestone in the battle against COVID-19.

“While millions of people have already safely received COVID-19 vaccines, we recognize that for some, the FDA approval of a vaccine may now instill additional confidence to get vaccinated,” Woodcock said in the agency’s press release.

President Biden also expressed the hope that the decision would provide encouragement to many of the 85 million eligible U.S. residents who until now have remained unvaccinated. 

“Let me say this loudly and clearly: If you’re one of the millions of Americans who said that they will not get the shot until it has full and final approval of the FDA, it has now happened,” he said in a speech on Monday. “The moment you’ve been waiting for is here. It’s time for you to go get your vaccination. Get it today.”

How many people will actually get vaccinated remains to be seen. However, experts are optimistic that full approval will sway at least a few people who until now have been on the fence.

“I do think it will make a difference,” Mark McClellan, director of the the Duke-Margolis Center for Health Policy and a former FDA commissioner, said in a press briefing on Monday, although he acknowledged that this might not translate into “a large number of people running out and getting a vaccine today.” 

For now, Pfizer’s vaccine is fully approved for those 16 and older, and will remain available under emergency use authorization to those 12 through 15 years old. When deciding whether to grant the vaccine full approval, the FDA examined data from tens of thousands of clinical trial participants, including about 12,000 who were followed for at least six months. Recent data found the shots to be 91 percent effective in preventing COVID-19, a slightly lower number than the 95 percent efficacy reported when the vaccine received emergency use authorization last December.

[Related: Here’s where all the COVID-19 vaccine candidates currently stand]

The FDA and the vaccine’s manufacturers will continue to monitor its safety over time, as is standard practice after a vaccine has been approved. This will include studies of myocarditis and pericarditis, rare side effects in which the heart muscle or its outer lining becomes inflamed. The conditions are usually mild and most people have recovered quickly.

“Full approval can reassure everyone that even though we’re in the midst of a pandemic, and it seems like things were happening quickly, the FDA is applying all of its gold standard regulatory approaches…everything it does in normal circumstances when we’re not in a pandemic,” McClellan said in the briefing.

Streamlining vaccination

In a recent poll from the Kaiser Family Foundation, 31 percent of unvaccinated respondents said they’d be more likely to get the COVID-19 vaccine once it had received full approval. However, what people say they’ll do doesn’t always line up with what they ultimately decide to do, says Silvia Saccardo, an assistant professor in the department of social and decision sciences at Carnegie Mellon University. 

She and her colleagues have studied how texting people reminders to get vaccinated affects their willingness and follow-through. They experimented with several kinds of messages. All of them contained links to appointment scheduling websites. Some texts also included an informational video about the vaccine, which was meant to give them confidence in the vaccine’s safety and effectiveness. Another kind of message, which was sometimes combined with the video, informed recipients that the vaccine had “just been made available for you” and encouraged them to “claim your dose.”

The team wanted “to understand whether making people feel like the vaccine is already theirs, it’s there for them, can boost their motivation further,” says Hengchen Dai, an assistant professor at the UCLA Anderson School of Management and coauthor of the study. 

Dai, Saccardo, and their colleagues conducted an online survey in which they asked more than 3,100 people how interested they’d be in getting the vaccine after receiving one of the texts from their healthcare provider. People who viewed the video were slightly more likely to express interest in the vaccine, while the language had no effect on their intentions. 

However, when the researchers actually sent the messages to more than 74,000 people eligible for vaccination, and then tracked whether they booked an appointment and got the vaccine, they found the opposite effect. “Just relying on what people say they will do is not enough,” Saccardo says. “It’s really important to see what works in the field.”

Overall, people who received a text reminder were 84 percent more likely to book an appointment than those who didn’t. Messages that included language meant to increase people’s sense of ownership over the vaccine had the strongest impact on increasing vaccinations. On the other hand, there was no additional boost from the informational video.

There are many potential explanations for the video’s disappointing performance, Saccardo says. One is that many people simply didn’t watch it, whether because they were busy or because they’d already decided to remain unvaccinated and didn’t want to be persuaded. Others may have wanted to wait until the vaccine received full FDA approval. And some participants might have been more receptive to hearing the information from someone they felt a connection to, such as a person from the same political party. 

[Related: US COVID-19 cases have nearly tripled in the past month]

It’s also possible that information about the vaccine would be more helpful in the form of messages tailored to the recipient’s concerns, Dai says. “Providing a quick piece of information directly in the text message based on their key concern or key question might be more useful than having them opt to watch a two-minute video seeking the response to their question,” she says.

Still, the findings, which were published on August 2 in the journal Nature, demonstrate that simple nudges such as text messages can increase vaccination rates. The researchers haven’t studied the role of full FDA approval of COVID-19 vaccines, but Saccardo is hopeful that some people will take it as their cue to schedule an appointment. 

“Right now the approval might actually work in persuading these people who stayed hesitant despite receiving information about the effectiveness,” she says. “A lot of people might be like, ‘Okay, now I can do it,’ [but] they might need to be nudged to do it, and then the findings of our research might become relevant.”

Once people are open to getting the shot, they may procrastinate or struggle to find time to schedule their appointment. “Making it as easy as possible seems to be important for moving the needle and getting people to just do it,” Saccardo says.

The full approval of Pfizer’s vaccine will also prompt more institutions such as the military, businesses, hospitals, and universities to make COVID-19 vaccines mandatory for employees and students.

These mandates will “bump up our vaccination numbers,” McClellan said in the briefing. “Companies who could do it before, I think they’re going to be more confident now and I think they’ll get more acceptance from their workers.”

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