Originally Published: 14 JUL 21 03:43 ET

Updated: 14 JUL 21 14:43 ET

By Madeline Holcombe, CNN

(CNN) -- Children will likely pay the price for adults in the US not getting vaccinated at high enough rates to slow or stop the spread of Covid-19, which has been surging in most states, a vaccine expert said.

If vaccination rates among adults and kids 12 and older keep lagging amid increased spread of the Delta variant, the youngest members of the population will be most affected, said Dr. Peter Hotez, a vaccinologist and dean of the National School of Tropical Medicine at Baylor College of Medicine.

"Transmission will continue to accelerate ... and the ones who will also pay the price, in addition to the unvaccinated adolescents, are the little kids who depend on the adults and adolescents to get vaccinated in order to slow or halt transmission," he said.

In 46 states, the rates of new cases this past week are at least 10% higher than the rates of new cases the previous week, according to data from Johns Hopkins University.

In Los Angeles County, the country's most populous, there has been a 500% increase in cases over the past month, according to the county's latest health data.

As cases increase, only 48.1% of the population is fully vaccinated, according to data from the US Centers for Disease Control and Prevention. And though many may brush off the risk of low vaccination rates to children, citing their low Covid-19 mortality rates, Hotez said they are still at risk for serious complications.

In Mississippi, seven children are in intensive care with Covid-19, and two are on ventilators, State Health Officer Dr. Thomas Dobbs tweeted Tuesday evening. Many more adolescents could be hospitalized, Hotez said, adding that up to 30% of children infected will develop long-haul Covid-19.

Nationwide, the overall number of new daily Covid-19 hospitalizations will likely increase over the next four weeks, an ensemble forecast published Wednesday by the CDC projects. There will likely be 2,100 to 11,000 new confirmed Covid-19 hospital admissions on August 9, the forecast says. Hospitalizations had been on a steady decline since late April, US Department of Health and Human Services data shows.

Scientists also are now learning about neurological consequences to long-haul Covid-19, Hotez said. Some studies have shown impacts on the brain of people who have been infected with the virus. One study in April found 34% of Covid-19 survivors received a diagnosis for a neurological or psychological condition within six months of their infection.

"What you're doing is your condemning a whole generation of adolescents to neurologic injury totally unnecessarily," Hotez said. "It's just absolutely heartbreaking and beyond frustrating for vaccine scientists like myself to see this happen."

Debate over vaccine mandates

With experts stressing the importance in vaccinating a majority of Americans against the virus, some officials are debating whether to mandate vaccinations at the local level. Some schools and employers have already implemented measures requiring students and employees to be vaccinated before returning.

Last month, Morgan Stanley announced unvaccinated employees, guests and clients would be banned from its New York headquarters. In April, Houston Methodist, a network of eight hospitals, said it would require all of its employees to get vaccinated. Of the 26,000 employees, 153 resigned or were fired as a result of refusing the vaccine.

That same month, the American College Health Association issued a policy statement recommending Covid-19 vaccination requirements for all on-campus college and university students for the upcoming fall semester, where state law and resources allow.

But many states are moving to block such requirements.

At least seven states -- Alabama, Arkansas, Florida, Indiana, Montana, Oklahoma and Utah -- have enacted legislation this year that would restrict public schools from requiring either coronavirus vaccinations or documentation of vaccination status, a CNN analysis found.

Such legislation can hurt the nation's 48 million Americans under the age of 12, former Secretary of Health and Human Services Kathleen Sebelius said Tuesday. Currently, Covid-19 vaccines are only available in the US to people 12 and older. Vaccine trials are underway for children 6 months through 11 years old.

"If we start with a lens on the children and wanting children to get back to school, which is what we all say is the priority, then we have to get more serious about employers and schools and universities stepping up and saying, 'It's great if you don't want to be vaccinated. But if you don't, you really can't have access to places that will put you in contact with folks who can't get vaccinated,'" Sebelius said.

The CDC announced last week it prioritizes in-person learning, even if all Covid-19 safety measures aren't in place. As K-12 schools will have a mix of vaccinated and unvaccinated people, it's necessary to layer strategies such as masking, physical distancing and, most importantly, vaccinations for everyone eligible -- people age 12 and older, the agency said.

The federal government can support vaccine use by expediting the full approval of available vaccines, Sebelius said. Vaccines are now available in the US under emergency use authorization.

"Getting full approval -- getting out of the emergency use authorization and into full approval -- is something that will clear up any legal questions that private employers may have," she said.

What surges could mean for the school year

Most officials and health experts have stressed the importance of students being able to safely return to school in the new academic year, but vaccine hesitancy could impact how districts move forward.

Only a quarter of Americans age 12 to 15 are fully vaccinated against Covid-19, according to data published Tuesday by the CDC, making them the age group with the lowest rate of vaccination.

California's K-12 schools were directed Monday to turn away students from campuses for refusing to wear face coverings in class, but the rules were revised just hours later to give schools more leeway in implementing protocol.

Despite the initial guidance stating, "Schools must exclude students from campus if they are not exempt from wearing a face covering under (California Department of Public Health) guidelines and refuse to wear one provided by the school," Alex Stack, spokesperson for Gov. Gavin Newsom's office, insisted the intent was not to turn away students.

"The way (the guidance) was written didn't accurately reflect the intent, so it was rewritten," Stack told CNN, acknowledging the statement came across as "banning kids." "It's important to get this right so parents and students know what to expect going in to school year."

New York City Mayor Bill de Blasio said the city's guidance could change as the school year gets closer, but for now, families should assume masks will still be worn in schools come September.

"We've been constantly working with the CDC, but we also in this case have been very careful given everything the city has been through ... for now, we're sticking with the idea that, you know, wearing the masks is the smart thing to do in schools," de Blasio said.