Public health experts hoped that after the Food and Drug Administration approved Pfizer-COVID-19 BioNTech’s vaccine in August, vaccine uptake would skyrocket.

Unvaccinated Americans were not swayed by the vaccine’s transition from emergency use authorization to full approval, according to a study published Wednesday in JAMA Network Open.

Researchers from the University of Utah looked at data from the Centers for Disease Control and Prevention from July 25, a month before full FDA approval, to September 9, the day before President Joe Biden announced his vaccine mandate.

They estimated how many doses would have been administered based on the vaccination rate prior to full approval versus the actual recorded number. The authors of the study discovered that FDA approval was linked to a 36 percent increase in vaccinations, with the majority being second doses. They discovered that the initial doses were 16 percent lower than expected.

The findings of the study do not surprise health experts.

Dr. Jay W. Lee, a family physician and chief medical officer of Share Our Selves community health center in Orange County, California, who is not affiliated with the study, said, “The reason people get vaccinated has very little correlation with whether or not something is approved or an EUA.”

According to health experts, misinformation and misunderstanding about vaccines has played a large role in vaccine resistance and hesitancy, and most Americans have personal reasons for not getting the vaccine.

“Most public health people are kind of out of touch with the thinking of people who are resistant to the vaccine,” said Terrie Moffitt, professor of psychology and neuroscience at Duke University. “They keep assuming that if we just give these people more information that they’ll get vaccinations and what we’re seeing is that it’s not true.”

The authors of the study compared vaccine uptake in the United States to vaccine uptake in the United Kingdom, where Pfizer’s vaccine’s regulatory status was unaffected by the FDA’s approval. Vaccination rates in the United Kingdom, unlike in the United States, remained stable throughout the study period.

Three out of ten unvaccinated Americans said they would be more likely to get vaccinated if the FDA moved vaccines from emergency use to full approval, according to a Kaiser Family Foundation survey released in June.

Moffitt, on the other hand, believes that mistrust is at the root of hesitancy and resistance, based on her own research.

She was the lead author of a March study that used a database to track nearly 1,000 people born in 1972 and 1973 in a New Zealand town. Researchers asked participants to fill out a survey about vaccine intentions last year, shortly before vaccines became available in the country, and compared their responses to what they knew about their upbringing and personality style.

Many of the vaccine-resistant or hesitant participants, according to the Duke researchers, had negative childhood experiences that may have influenced their trust in authority. The same is likely true for Americans, according to Moffit.

“This has left them with a legacy of mistrust, particularly mistrust of the government,” Moffitt said. “Policymakers have really underestimated how deep-seated that mistrust is.” “We’re not going to break down the FDA’s wall of suspicion (approval). That’s a little overconfident.”

While FDA approval may not have had an impact on first doses, the University of Utah study discovered that it was linked to a 77% increase in second doses. This should not be overlooked, according to health experts, and suggests that full approval of COVID-19 vaccines may have some public benefit.

“The data suggests that approval is still important and communicates the vaccine’s safety to a lot of people,” lead author Elise Bailey, a PhD student at the University of Utah, said. “It appears to change some people’s behavior, regardless of how it changes their thinking.”