(CNN) — As the Delta variant rapidly spreads, US hot spots have seen climbing case numbers — and an expert warns a “surprising amount of death” from COVID-19 could soon follow.

The United States is averaging about 19,455 new cases over the past seven days, a 47% increase from the week prior, according to data from Johns Hopkins University. And a third of those, CNN medical analyst Dr. Jonathan Reiner said, come from five hot spots: Florida, Louisiana, Arkansas, Missouri and Nevada.

“In places like Missouri where ICUs are packed, you’re going to see a surprising amount of death,” Reiner said on Sunday.

At Mercy Hospital in Springfield, Missouri, 91% of patients in the intensive care unit are on ventilators and many are in their 20s, 30s and 40s, Chief Administrative Officer Erik Frederick told CNN on Saturday. That is especially concerning, he said, because at the peak last year there were only 40 to 50% of ICU patients on ventilators.

Typically, spikes in COVID-19 cases leads to a rise in death rates three to four weeks later as a small percentage of the infected are hospitalized and deteriorate. “We will start to see an increase in mortality in this country,” Reiner said.

What is particularly frustrating for many experts, Reiner said, is that the deaths are “completely avoidable” now that vaccines are available. But about one-third of those 12 and older in the United States haven’t received the vaccine yet, CDC data shows.

“The vaccines we have work really well against this variant. It doesn’t need to be this way,” Reiner said.

Dr. Howard Jarvis, an emergency medicine physician in Springfield, told CNN on Monday that his sick patients are all unvaccinated.

“If they’re sick enough to be admitted to the hospital, they are unvaccinated. That is the absolute common denominator amongst those patients,” he said. “I can see the regret on their face. You know, we ask them, because we want to know, are you vaccinated? And it’s very clear that a lot of them regret (not being vaccinated).”

Across the country, more than 99% of US COVID-19 deaths in June were among unvaccinated people, said Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention.

The pace of vaccinations has also dropped sharply in the past few months. About 246,000 people initiated vaccination each day over the past week, down 88% from the April peak, and about 278,000 people became fully vaccinated each day over the past week, down 84% from the April peak, CDC data shows.

“We really need to get more people vaccinated, because that’s the solution,” Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said Monday on “CBS This Morning.” “This virus will, in fact, be protected against by the vaccine.”

CDC, FDA looking into risk of nerve complication after J&J shot

Federal health officials are investigating the possibility that Johnson & Johnson’s coronavirus vaccine might slightly raise the risk of a rare neurological complication known as Guillain-Barré Syndrome (GBS), a spokesperson from the CDC said in a statement to CNN on Monday.

But even if the vaccine does raise the risk, it’s still better to get vaccinated, the CDC stressed.

“GBS is a neurological disorder in which the body’s immune system damages nerve cells, causing muscle weakness or in the most severe cases paralysis. Each year in the United States, an estimated 3,000 to 6,000 people develop GBS; it is typically triggered by a respiratory or gastrointestinal infection. Most people fully recover from GBS,” the spokesperson said.

“Reports of GBS after receipt of the J&J/Janssen COVID-19 Vaccine in the Vaccine Adverse Event Reporting System (VAERS) are rare, but do likely indicate a small possible risk of this side effect following this vaccine. Around 100 preliminary reports of GBS have been detected in VAERS after 12.8 million doses of J&J/Janssen COVID-19 Vaccine administered. These cases have largely been reported about two weeks after vaccination and mostly in males, many aged 50 years and older.”

The same pattern is not seen with the other two vaccines authorized in the United States, made by Moderna and Pfizer. The spokesperson said the CDC’s Advisory Committee on Immunization Practices would discuss the matter in an upcoming meeting.

Pfizer to brief the US on boosters

Another concern for many experts as variants spread is whether the population will need boosters for their vaccines.

Pfizer will virtually brief US government officials Monday evening regarding the potential need for booster shots of its COVID-19 vaccine, a company spokesperson and two administration officials confirmed to CNN.

The meeting is seen as a courtesy, and federal guidance on boosters is not expected to change immediately following the meeting, a senior health official said.

Last week, Pfizer/BioNTech reiterated its expectation that people may need boosters to its vaccine in six months to a year, citing waning immunity they are seeing among people who got it. The company also said it would seek emergency use authorization in August from the US Food and Drug Administration for a booster.

But some experts have argued the data is showing boosters are not necessary yet.

“Americans who have been fully vaccinated do not need a booster shot at this time,” the US Centers for Disease Control and Prevention and the FDA said. “FDA, CDC, and NIH (the National Institutes of Health) are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary.”

Fauci also disputed the need at this time.

“Given the data and the information we have, we do not need to give people a third shot, a boost, superimposed upon the two doses you get with the mRNA (Pfizer/BioNTech and Moderna vaccine) and the one dose you get with (Johnson & Johnson),” he told CNN on Sunday.

Further, World Health Organization leaders asked wealthy countries Monday to hold off on giving booster doses to their residents before people in other countries can even get their first doses.

“Instead of Moderna and Pfizer prioritizing the supply of vaccines as boosters to countries whose populations have relatively high coverage, we need them to go all-out to channel supply to COVAX, the Africa Vaccine Acquisition task team, and low- and middle-income countries, which have very low vaccine coverage,” WHO Director-General Dr. Tedros Adhanom Ghebreyesus said in a media briefing.

Experts weigh whether vaccinations should be mandated

In the United States, the now-dominant Delta variant, which is believed to be more transmissible, has driven the rising case numbers. And the variant has sparked discussions over local vaccination mandates.

Across the country, 48% of the population is fully vaccinated, but in some states that number is much lower, according to CDC data. Alabama, Arkansas, Louisiana, Wyoming and Mississippi all have around 35% or less of their populations fully vaccinated.

Experts say vaccines are key to managing spread. With information changing rapidly, it is important to be smart about how vaccinations are mandated, George Washington University School of Medicine professor Dr. Gigi El-Bayoumi said.

“In states where there are high vaccination rates, that are like 75 or above, it makes sense to loosen up the restrictions. In places where there are not, such as some of the Southern states, it makes sense” to mandate vaccinations, El-Bayoumi said Sunday.

Mandates at the local level are a good idea, Fauci told CNN.

“We’re talking about life and death situation. We’ve lost 600,000 Americans already, and we’re still losing more people. There’ve been 4 million deaths worldwide,” Fauci said. “This is serious business.”

Fauci expects vaccine mandate hesitancy to lift when vaccines are fully approved, he said.

Right now, COVID-19 vaccines are being administered under emergency use authorizations, which Fauci said has made some people skeptical as to their safety and efficacy. But the amount of data that supports the importance and safety of the vaccines is more than anything experts have seen for an EUA, he said.

“These vaccines are as good as officially approved with all the I’s dotted and T’s crossed,” Fauci said.

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