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.

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“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.

“Every single patient that we’ve admitted for Covid is not yet fully vaccinated,” County Health Services Director Dr. Christina Ghaly told the Board of Supervisors on Tuesday.

The health department runs four hospitals, including those affiliated with the University of California-Los Angeles and the University of Southern California, along with 19 health care centers throughout the region.

As cases increase nationally, only 48.2% of the population is fully vaccinated, according to data from the 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.

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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.

Study suggests why Delta variant is more contagious
The Delta variant might spread faster than other strains of the novel coronavirus because it makes more copies of itself inside people’s bodies quicker than other strains of the coronavirus.

In research posted online last week, Chinese scientists detected on initial positive tests Delta viral loads that were about 1,260 times higher than earlier strains. They compared 62 Delta cases with 63 cases from the early epidemic wave in 2020.

Moreover, the amount of time it took quarantined people to test positive for coronavirus on PCR also shortened — from about six days with the earlier infections to four days with Delta.

“These data highlight that the Delta variant could be more infectious during the early stage of the infection,” the researchers wrote.

According to Public Health England, a number of analyses have shown Delta to be more transmissible, including lab studies that suggest “increased replication in biological systems that model human airway, and evidence of optimised furin cleavage” — a process that activates the virus’ entry into the human cell. The variant has also been observed to spread faster in real-world epidemiological studies.

According to the World Health Organization, Delta is estimated to spread roughly 55% faster than the Alpha variant first identified in the UK, and roughly twice as fast as variants that do not rise to the level of “interest” or “concern.”

Heath officials have said that cases caused by the Delta variant in fully vaccinated people are rare and the strain is for the most part only causing severe disease and death in unvaccinated people.

And health officials aren’t just concerned about the Covid-19 risks for people who are unvaccinated, but also the risks for a significant number of people who are partially vaccinated — especially those who are overdue for their second dose or skipped their second-dose appointments.

The Pfizer/BioNTech and Moderna coronavirus vaccines are administered as two doses, 21 and 28 days apart, respectively. Studies have shown that those vaccines are much more effective against the Delta variant after completion of the two-dose series. People who have received one dose should still follow Covid-19 mitigation steps, such as wearing masks, until they are fully vaccinated.

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