As the U.S. heads into year three of the coronavirus pandemic, cases have now surpassed 49.9 million in the country and 270.2 million worldwide.

Most of these cases, especially the more severe ones, are among those who are still unvaccinated.

“We talk endlessly about booster dosing but the fact of the matter is the real problem right now in this country is we need to vaccinate the unvaccinated,” Dr. Paul Offit, attending physician and director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, said on Yahoo Finance Live (video above). “That’s the issue.”

Currently, 60.8% of the total U.S. population is fully vaccinated while 72% have received at least one dose, according to CDC data. These numbers have slowed over the past few months, worrying many public health experts as the country heads into another winter season.

“We’re not going to boost our way out of this pandemic,” Offit stressed. “What we need to do is find a way to vaccinate the unvaccinated, and don’t give up on that. I have to believe there’s a way to make this happen.”

Cases hit an all-time high last winter as more people were driven indoors due to cold weather and therefore more exposed to others carrying the virus.

“Unfortunately, we’ve been here before,” Dr. Payal Patel, an infectious disease physician at the University of Michigan, recently told Yahoo Finance. “One year later, we’re back where we were a year ago. A lot of things have changed. The biggest things that have changed are the vaccines that are available.”

What booster shots do, Offit explained, is provide additional protection against mild illness. For those who are skeptical about the efficacy of vaccines, he noted that vaccinations protect against serious illness and that adding boosters to the mix is common with a virus.

“I think we expect way too much when we’re trying to prevent mild illness,” he said. “We expect that of no other vaccine, whether it’s a so-called mucosal vaccine like [that for] rotavirus or influenza or whooping cough. Those vaccines are not very good at protecting against mild illness or asymptomatic infections. So I think we’ve held this vaccine to a much higher standard. We should be reassured by the fact that hospitalizations and deaths are going down. That’s what you want to make sure happens.”

'What I saw was children struggling to breathe'

Children — who were initially seen as a low-risk population group — are now experiencing more and more cases of COVID.

According to the latest data from the American Academy of Pediatrics, nearly 7.2 million children have gotten COVID since the start of the pandemic, as of Dec. 9, with a 24% increase in cases from the prior week. During that time span, children accounted for 23.6% of weekly reported cases.

“I was on service about a week and a half ago and during that week that I was on service, we saw a lot of children admitted to our hospital,” Offit said. “Most were over 5. Many were over 12, and certainly there were a handful that had to be admitted to the intensive care unit. What all of those children had in common is although most of them could have been vaccinated, none of them were — nor were their parents, nor were their siblings.”

Vaccines are now approved by the FDA for children over the age of 5, and Offit strongly encouraged parents to make sure their children receive their dose.

“What I saw was children struggling to breathe, with three liters of face mask oxygen or nine liters, still having low oxygen in their bloodstreams, being wheeled up to the intensive care unit, sedated with a tube put down into their windpipe attached to a ventilator,” he said. “You see parents crying and no one’s vaccinated. It’s just really frustrating and I think we’re in some ways numbed by the statistics. … Honestly, if people saw what I saw last week, I can’t believe anybody would then still choose not to vaccinate a child.”

Because the virus is constantly mutating as it’s able to circulate between humans, the best solution is to make sure you and your loved ones are vaccinated, according to both Offit and Patel.

“Some of those unvaccinated are kids and babies and young adults,” Patel said. “But the vaccine has now been out for young adults and kids for a while. I really think that, especially right now, instead of watching and waiting, parents really need to be thinking about getting their kids vaccinated. That’s going to lead to a much easier winter and then hopefully, an easier beginning of the next year as well for the whole family.”

Adriana Belmonte is a reporter and editor covering politics and health care policy for Yahoo Finance. You can follow her on Twitter @adrianambells and reach her at adriana@yahoofinance.com.

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