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Covid-19 hospitalizations are reaching all-time highs in parts of the South, with some patients unable to get the care they would normally receive.

Susan Walker has been calling out-of-state hospitals trying to get help for her husband, who did not get vaccinated against Covid-19 and is now in a medically induced coma.

“He is on a ventilator and in dire need of an ECMO treatment, which is not available at the hospital that he is in,” the Florida mother said Sunday.

“All the beds are taken up by Covid victims also getting ECMO.”

An ECMO treatment uses external machinery that can function as the heart and lungs. It’s been used with some severely ill Covid-19 patients, including young adults.

“We have searched every hospital from the south of Florida to the north part of Florida” trying to find availability, Walker said.

“To transfer him to a hospital in Florida is next to impossible.”

Across the country, states are struggling to fend off the Delta variant – the most contagious strain of coronavirus yet.

But the situation in particularly worrisome in several Southern states.

Louisiana set a new record for Covid-19 hospitalizations last week.

Florida’s hospitalizations recently jumped 13% above the state’s previous peak on July 23, 2020, according to a survey by the Florida Hospital Association.

The FHA said it expects 60% of the state’s hospitals to face a “critical staffing shortage” by this week.

And at Houston’s United Memorial Medical Center, “We have no beds. The emergency department is full of patients just waiting to be able to get into the hospital,” Chief of Staff Dr. Joseph Varon said Sunday morning.

“Over the last 12 hours, we have lost more patients than … in the last five to six weeks.”

According to data published Sunday by the US Centers for Disease Control and Prevention, 50.1% of the total US population is now fully vaccinated – more than 166 million people.

As of Sunday, Mississippi has fully vaccinated 35.2% of its residents. That makes Alabama – with 34.8% of its residents fully vaccinated – the only state in the US to have fully vaccinated less than 35% of its residents.

The seven-day average of doses administered each day is now 706,323 doses, per the CDC data, and an average of 449,000 people are initiating vaccination each day.

More hospitalizations and deaths expected

The US now is averaging more than 100,000 new Covid-19 cases every day – the highest in almost six months, according to data from Johns Hopkins University.

Because it can take days or weeks for some Covid-19 cases to lead to hospitalization or death, doctors are bracing for an ugly repeat of scenes from 2020.

“It’s bad. For me, this is a deja vu of what we had last year,” Varon said.

“And the worst part about this is this was foreseeable. And this was preventable. So not only are (we) exhausted, we’re annoyed. And we’re annoyed because people are not doing the right thing.”

The vast majority of those getting hospitalized with or dying from Covid-19 are not fully vaccinated, Dr. Rochelle Walensky, the director of the CDC, said last week.

And Americans who have already had Covid-19 shouldn’t assume they don’t need a shot.

For adults previously infected with Covid-19, vaccines give better protection against reinfection than natural immunity on its own, according to a CDC study published Friday.

The study suggests people who got Covid-19 in 2020 and didn’t get vaccinated were more than twice as likely to be reinfected in May or June 2021, compared with people who also had Covid-19 but were later fully vaccinated.

“If you have had Covid-19 before, please still get vaccinated,” Walensky said Friday.

There is no minimum time to wait between recovering from Covid-19 and getting vaccinated, the CDC said.

“Getting the vaccine is the best way to protect yourself and others around you,” Walensky said, “especially as the more contagious Delta variant spreads around the country.”

Children’s hospitals are getting overwhelmed

Almost half the country is not fully vaccinated, including children under 12 who are not yet eligible but are still vulnerable to Covid-19.

Scientists say the Delta variant is as contagious as chicken pox, with each infected person potentially infecting eight or nine other people.

Delta may also cause more severe disease than other strains of coronavirus, according to studies cited in an internal CDC presentation.

Now some hospitals are seeing younger Covid-19 patients than before.

“Something very scary now is happening in the Southern United States. We are seeing this massive surge of hospitalizations of young people that we’ve never seen before in hospitals across the South,” said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.

“It’s many, many young people, including, I’m sorry to say, many children’s hospital admissions. And for the first time that I can remember, we’re starting to see pediatric intensive care units get overwhelmed, which we never really saw before.”

As of Tuesday, an average of 192 children with Covid-19 were admitted to US hospitals every day over the past week, CDC data shows.

That’s a 45.7% increase from the previous week in daily new hospitalizations among Covid-19 patients ages 0 to 17.

In the Miami area, “our children’s hospitals are completely overwhelmed,” said Dr. Aileen Marty, an infectious disease expert at Florida International University.

“Our pediatricians, the nursing, the staff are exhausted. And the children are suffering,” Marty said.

“It is absolutely devastating … We’ve never seen numbers like this before.”

In Texas, Ava Amira Rivera – an 11-month-old Covid-19 patient – had to be airlifted to a hospital 150 miles away because of a shortage of pediatric beds in the Houston area.

None of the major pediatric hospitals in the area had beds available, said Amanda Callaway, a spokeswoman for Harris Health System.

The baby’s condition has since stabilized, and she is no longer intubated.

Who might need booster doses first

With more than 164 million Americans fully vaccinated, tens of thousands might get Covid-19 later on, Walensky said.

Even though there’s no coronavirus in any of the vaccines used in the US, breakthrough infections are expected – like with other vaccines.

Those who do get breakthrough infections generally have mild or no symptoms. As of late July, more than 99.99% of fully vaccinated Americans have not had a Covid-19 infection leading to hospitalization, according to CDC data.

The tiny fraction of breakthrough infections that do lead to hospitalization can include those who are immunocompromised or elderly.

Those two groups may be among the first to get an additional dose of vaccine, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

Because the Covid-19 vaccines require an immune response to work, those who are immunocompromised or taking immune-suppressing drugs might not get adequate protection with a vaccine.

“We will almost certainly be boosting those people before we boost the general population that’s been vaccinated,” Fauci said Sunday. “And we should be doing that reasonably soon, I believe.”

He said the next group that may need boosters sooner than the general population are those over age 60. Fauci said the CDC is studying different age groups to see how long vaccines may stay effective.

“As soon as they see that that level of durability of protection goes down, then you’ll see the recommendation to vaccinate those individuals,” he said.

Long-haul Covid victim: ‘I didn’t think I fit the profile’

Quentin Bowen said he had scheduled an appointment to get vaccinated but had to cancel because of work.

The 41-year-old farmer from Nebraska said he assumed delaying his vaccination wasn’t a big deal.

“I didn’t think I fit the profile of who Covid (could) attack,” Bowen said Saturday. “I was healthy. I was younger. And I was going to get (the vaccine). And I figured I’d been exposed to it before and never got it, so I thought I had time.”

But Bowen fell sick with Covid-19 in May. He recalled going to the hospital and asking his friend to tell his kids he loved them.

“I knew I wasn’t coming home that day. And I didn’t know if I’d come home ever,” Bowen said.

He survived a pulmonary embolism but is still struggling with complications three months later.

Bowen urged Americans to get vaccinated as soon as they can, when they still have the power to help preserve their health.

“Once you walk through the hospital door,” he said, “it’s all out of your hands.”

Correction: An earlier version of this story incorrectly described the capacity at Nicklaus Children's Hospital in Miami. The hospital, a 309-bed pediatric specialty hospital, had a total of 214 admissions on Saturday. Of those, 18 were Covid-19 positive and five were in intensive care units.

CNN’s Lauren Mascarenhas, Jessica Firger and Matthew Hilk contributed to this report.