(NEW YORK) — Since the updated bivalent COVID-19 booster was rolled out at the beginning of September, only 19.4 million Americans have received it as of Oct. 19, according to data from the Centers for Disease Control and Prevention.

The booster is designed to protect against the omicron subvariants BA.4 and BA.5, the latter of which still makes up most virus cases in the United States.

Initially rolled out to those aged 12 and older for the Pfizer booster and those aged 18 and older for the Moderna booster, eligibility was expanded to ages 5 and older for Pfizer and 6 and older for Moderna, about two weeks ago.

However, there are still an additional 200-plus million Americans who are eligible but have not yet gotten the booster.

So why is booster uptake lagging, especially among the older population who were the first to get their primary vaccination series?

Experts told ABC News that COVID-19 is not currently top of mind for many Americans and that public health officials and community leaders need to meet people where they are.

Dr. Benjamin Rosenberg, an assistant professor of psychology at Dominican University of California and director of the Health and Motivation Lab, thinks one reason for the lagging rate is because U.S. public health officials have focused too much on “bench science” — work conducted in a laboratory — and not “social science,” which studies people’s behaviors, thoughts and beliefs.

“The absence of social science from the pandemic response has been really noteworthy,” he told ABC News. “Most folks have a very clear idea of how COVID is transmitted and a lot of what drives up surges is human behavior.”

He continued, “Obviously variants emerge and are more contagious, our immunity wanes, but a lot of what drives surges is human behavior and so to not be talking to folks who study this is I think really a big, big mistake.”

Rosenberg said this means to increase booster shots, it’s not just a matter of a vaccination campaigns to get people to schedule appointments, but rather booster opportunities need to be offered in everyday health care locales, such as a pharmacy.

The pharmacist then should not just describe the complications that could arise if someone doesn’t get the shot but highlight the benefits of getting it as well, he explained.

“Those are places that we frequent, everybody’s going to the pharmacy for something or other,” he said. “So, it could really begin there where you walk in and, particularly if you are there to pick up a prescription or talk to a pharmacist about something, they can immediately check to see if you are up to date on your shots, specifically if you’ve gotten this most recent bivalent booster.”

Rosenberg continued: “And if you haven’t, they can basically say, ‘Hey, do you want to get this right now?’ Give you that opportunity, sort of capitalize on the fact that they know you haven’t gotten it and with that provide you some accurate information about the benefits of getting it. You know, that protection will offer you the other benefits, like social things, that you could enjoy your holidays with your family a little bit more freely.”

Dr. William Schaffner, a professor of preventive medicine at the Vanderbilt University Medical Center, agreed and said people need to have trusted leaders also explain the benefits of the vaccine to communities that are more hesitant.

Rather than trying to get people to schedule an appointment at a pharmacy or a doctor’s office, this could involve setting up town halls or other community events.

“To have people coming from those communities, who are like them in every way to actually demonstrate they’re personally receiving the vaccine, they provide that level of comfort or assurance, that this is a good thing to do for themselves and their families and their communities,” Schaffner told ABC News. “So, we need many, many more ambassadors to reach wonderful diversity of populations that we have in this country.”

Schaffner continued, “It works better if there are leaders, medical leaders, religious leaders, political leaders, people who are thought to be older and wiser in those communities to just go out there.”

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