Children are now being hospitalized in record numbers in the US, and doctors are warning it could get worse if schools reopen and the fast-moving coronavirus delta variant increases cases.

New Covid hospital admissions for children have reached their highest level since the US started tracking pediatric cases about a year ago, averaging 303 new admissions per day for the week ending August 22, according to data from the Centers for Disease Control and Show prevention.

With most students not old enough to get the syringes, doctors and epidemiologists fear the surge in Covid hospital admissions could get worse unless more children get vaccinated and school districts mandate masks and other safety precautions in class .

“It’s scary to see the number and severity of Covid-19 cases in children with the Delta variant increase and so many children still remain unprotected,” said Dr. Nusheen Ameenuddin, a pediatrician at the Mayo Clinic. “The pandemic never stopped, and unfortunately all it takes is a lighted match to rekindle the inferno.”

Children still make up a very small number of hospital admissions, doctors note, which accounts for about 1.8% of all Covid hospital admissions in the U.S. The virus just doesn’t hit kids as hard as it does adults. They are less infected with Covid than other age groups and usually have milder symptoms. Of more than 520,000 Covid deaths for which the CDC has demographics, fewer than 500 were children under the age of 18.

Still, some children with Covid can end up in hospital. About 4,404 children have a rare but severe inflammatory syndrome caused by Covid, known as MIS-C; 37 died of it, according to the CDC.

At Wolfson Children’s Hospital in Jacksonville, Florida, 15 children with Covid were hospitalized, six of them in intensive care, according to the facility. The hospital has reported 71 pediatric admissions so far this month and 87 admissions in July, more than the 49 admissions reported during the ward’s previous surge in January.

Dr. Mobeen Rathore, a local epidemiologist, said they were prepared for more cases.

“There were 503 cases of coronavirus in Duval County’s public schools in the first nine days of school,” Rathore said. “We are preparing not only for acutely ill children, but also for MIS-C. We update our protocols and plans for people, facilities and care for each increase.”

Oklahoma, Ohio, Louisiana, and Kentucky have the highest pediatric hospital admissions when you factor in population, according to data compiled by the Department of Health Human Services. These states all have vaccination rates below the national rate, according to the CDC.

While Delta is much more contagious than previous variants, causing a surge in pediatric hospital admissions, it doesn’t appear to cause any more serious illness in children so far, said Sunitha Kaiser, a pediatric nurse at the University of California, San Francisco.

“We only have maybe six or eight weeks of data on the delta and that picture will evolve over time,” Kaiser said in a telephone interview. “But from what we’ve seen so far, it does the same thing in our body in terms of how the infection works, how it penetrates, and the similar severity and symptoms to previous exposure.”

She said vaccinations are still the best strategy to protect children and the community because vaccinations are so effective in preventing serious illness, hospitalizations and deaths. “This contagion can be contained again by achieving higher and higher vaccination rates,” she added.

Pfizer and BioNTech’s Covid vaccine has been FDA approved for emergency use in children 12-15 years old as scientists collect more data on that age group. It is fully approved for people aged 16 and over. Moderna’s vaccine is approved for adults only, but is expected to soon be approved for use in 12 to 17 year olds.

About 62.5% of all adults in the US are fully vaccinated, but only 44% of 16- and 17-year-olds are fully vaccinated against Covid, according to the latest data from the CDC on Monday. Only 34% of children between the ages of 12 and 15 have all had their Covid vaccinations – the lowest of all age groups currently eligible for the vaccine, the data shows.

Dr. Paul Offit, a doctor at Children’s Hospital of Philadelphia, where doctors are also seeing an increase in pediatric hospital admissions, said he was frustrated with lower vaccination rates in children.

“Yes, it’s true that we don’t have a vaccine for children under the age of 12 yet, but we have one for those aged 12-17 and it’s only about 30% of the intake,” he said.

He said federal and state health officials should focus on convincing unvaccinated parents to get the shots, as they are often the ones who make the decision about whether their children can do it.

Ameenuddin of the Mayo Clinic said it was important to her to ask her patients and families if they received the vaccine.

“Most legitimate people have said yes, which is comforting, and even asked when it will be available to the younger folks,” she said.