(CNN) -- With COVID-19 cases rising and vaccination rates on the decline, health experts say they are concerned about the next chapter in the pandemic -- especially for younger Americans, who they say are feeling the impacts.

"We do know that in our ICUs, we are seeing younger people intubated who are very sick or who are on the floors and are very sick," Dr. Jeanne Marrazzo, professor of infectious diseases at the University of Alabama at Birmingham, said. "That should be a gigantic wake-up call."

With one of the lowest vaccination rates in the country, Marrazzo said Alabama is "at the beginning of a wildfire" when it comes to Covid-19 spread. And like many other health professionals in states with low vaccination rates, she said she desperately hopes stories and data showing the impact of the virus will motivate younger people to get vaccinated.

Ensemble forecasts from the US Centers for Disease Control and Prevention published Wednesday project Covid-19 deaths and hospitalizations will likely increase over the next four weeks.

Meanwhile, vaccinations rates, which health experts have emphasized as a key part of the plan to get the virus under control, are down to the lowest they have been since January, with 516,441 doses on average reported administered each day of the past week, according to the CDC.

Nationally 48.8% of people are fully vaccinated, but some states, like Alabama with 33.9% and Arkansas with 35.5%, are particularly struggling to get a high enough vaccination rate to slow or stop the spread of the virus, according to the CDC.

That is especially heartbreaking, two doctors say, when patients decide they want the vaccine too late.

"What I really wish you could see, is to look into the eyes of a young father or a gentleman who knows that they may be short for this world because they didn't get their vaccine, and the regret and remorse on their face -- and fear," Dr. Michael Bolding at Arkansas' Washington Regional Medical Center said in a video he made to beg Arkansas residents to get vaccinated.

A doctor in Alabama said one of the last things her patients do before they are intubated due to COVID-19, is beg her for the vaccine, but she has to tell them it's too late.

When those patients die and she talks to their family, they tell her they thought the virus was a hoax, Dr. Brytney Cobia of Grandview Medical Center said in a Facebook post. She said she tells them the best way to honor their loved one is to get vaccinated.

"I go back to my office, write their death note, and say a small prayer that this loss will save more lives," Cobia wrote, urging people to ask her questions about the vaccine. "It's not too late, but some day it might be."

COVID-19 has unvaccinated people 'in its sights,' expert says

Although health officials are worried about the spread of the more transmissible Delta variant, experts like National Institutes of Health Director Dr. Francis Collins said those who are vaccinated are still well protected.

The same is not true, he said, for unvaccinated Americans.

"For those who are not vaccinated, this is becoming a pandemic that has you in its sights," Collins told CNN's Jim Acosta Wednesday.

"We are in for trouble, as CDC's projections have laid out, in the coming weeks, especially in those parts of the country where vaccination rates are low and Delta is widespread," Collins said.

The US is now averaging 34,056 new COVID-19 cases each day, according to data from Johns Hopkins University -- a 55% increase over last week. And some areas are faring even worse.

Los Angeles County reported 2,551 new coronavirus cases Wednesday, a 20-fold increase in a month, according to the public health department. Just one month ago, the Los Angeles County Department of Public Health reported 124 new cases.

The spread of COVID-19 not only has consequences for those that it directly infects, but it also increases the risk for new variants to form, said Dr. Paul Offit, a member of the US Food and Drug Administration vaccine advisory committee.

"The virus will continue to reproduce itself, continue to cause suffering and hospitalization, and worse still, continue to have the chance to make variants that are much more resistant to vaccine-induced immunity," Offit said.

Vaccines are the strongest tool, but mask policies may help

The risk coming from increased spread and not enough vaccination has pushed some leaders to advocate for a return to mask policies.

Former US Surgeon General Dr. Jerome Adams said in an opinion piece published in the Washington Post that the CDC "urgently needs to revise its guidance on masking to combat the rapid growth in covid-19 infections driven by the delta variant."

Vaccinations are the strongest tool to fight the virus, he said, but rates are still too low and "with many communities -- particularly communities of color -- at risk for yet another devastating wave of cases, hospitalizations and deaths, masks are the next best tool that officials have in places where vaccination levels remain low despite covid cases rapidly rising."

A study published Wednesday in JAMA Network Open found that protective measures -- like masks, handwashing and physical distance -- help protect against the spread.

Among more than 500 essential workers who continued to work at Colorado State University in Fort Collins through the first six months of the pandemic, not one tested positive for COVID-19 in the months that were studied.

In places like New Orleans, leaders have returned to advising residents to wear masks indoors when they're with people outside of their immediate household.

Meanwhile, Texas Gov. Greg Abbott said he will not be implementing another mask mandate. He told CNN affiliate KPRC he believes enough immunity has been acquired through vaccines or exposure that it would be inappropriate to force people who are already immune to wear a mask.

According to CDC data, 43.1% of the Texas population is fully vaccinated. The CDC advises people should get vaccinated regardless of whether they've had COVID-19 and many doctors believe the immunity you get from vaccination is likely stronger than the immunity you get from previous infection.

The-CNN-Wire™ & © 2021 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.

CNN's Naomi Thomas, Deidre McPhillips, Lauren Mascarenhas, Sarah Moon, Ben Tinker & Jacqueline Howard and Kay Jones contributed to this report.

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