President Joe Biden pleaded with unvaccinated Americans to get their COVID-19 shots, as he rolled up his sleeve for his third dose Monday.

"The most important thing we need to do is get more people vaccinated," he said, adding that it is now a pandemic of the unvaccinated.

Biden cited the needed recovery of the U.S. economy and overall safety and protection of fellow Americans.

"About 23 percent haven't gotten any shots. And that distinct minority is causing ...an awful lot of damage to the rest of the country," the president said.

"We know that to beat this pandemic and to save lives, to keep our children safe, our schools open, our economy going, we need to get folks vaccinated," he added.

But convincing the unvaccinated, and targeting their reasons for hesitation or refusal, is not an easy task.

CDC Director Dr. Rochelle Walensky told Yahoo Finance the agency is hard at work to identify the issues.

"We can't characterize all people who haven't gotten the vaccine as the same," she said.

A recent New York Times column showed Republican states were among the least vaccinated, adding to reporting in recent months that COVID-19 cases were highest in these states among the unvaccinated.

Dr. Ashish Jha, dean of the Brown University School of Public Health, has said such classifications are not helpful. He noted that labeling unvaccinated by political ideology conflates any underlying issues — such as barriers to access or hesitations — with politics.

"Then we've taken access and barriers and converted that into a political identity," Jha said.

But it goes beyond that, according to Dr. Oni Blackstock, a physician and founder and executive director of Health Justice.

"It's not just about political leanings," Blackstock told Yahoo Finance, saying there are other characteristics of a specific subset of the population that refuse to be vaccinated.

"Personal freedom and individualism...are core values of this culture that is quite destructive but isn't often called out," she said.

And, Blackstock added, misinformation and disinformation campaigns have taken advantage of these ideas, "working to exacerbate or amplify divisions that already exist."

Walensky said studies have shown a myriad of reasons for the unvaccinated.

"Survey studies have shown that people have different reasons for not yet getting vaccinated. And we have to address those people one at a time for the reasons that they have," Walensky said.

If they want to see safety data, there are now nearly 6 billion people vaccinated globally, with over 180 million in the U.S. — which means lots of data to pull from. If they know someone who was vaccinated but still got sick, or who got sick from the vaccine, what kind of information do they need to understand what happened and what the risks are?

Walensky noted that the pushback to vaccinations was not a surprise and was anticipated even as the mass vaccination sites were being rolled out.

"We knew...people were not going to be coming up rolling up their sleeves, and that we were going to have to get down to the community level. And that's the hard work we continue to do every single day," Walensky said.

That includes working with trusted community leaders, influencers and micro influencers, as well as working with community- and faith-based organizations.

"I think every single person has potentially unique reason for why he or she ... has not been vaccinated. And that's the hard work that we need to do."

Follow Anjalee on Twitter @AnjKhem

Read the latest financial and business news from Yahoo Finance.

Follow Yahoo Finance on Twitter, Facebook, Instagram, Flipboard, SmartNews, LinkedIn, YouTube.