Just days after the start of their academic year, over 20,000 pupils from 800 Mississippi schools have been told to quarantine due to COVID exposure.
Some 4,500 children became sick with COVID during this first week of school.
Across the US, states like Mississippi with low vaccination rates and relaxed mask rules have asked thousands of students and staff to quarantine.
The Delta variant, the dominant strain in the US, has been affecting younger people at a higher rate.
The US has recorded about 4.4m child infections – out of a total of 37 million – since the pandemic began.
Fewer than two per cent of child COVID-19 cases require hospital admission, according to the American Academy of Pediatrics, and no more than 0.03 per cent of all such cases in the US have resulted in death.

Children under 12 are not yet approved to be vaccinated in the US, putting them at a higher risk of catching the highly contagious variant.
Infections and hospital admissions are on the rise among the young in a way not seen earlier in the pandemic, when the virus was mostly affecting the elderly and people with pre-existing health conditions. In Mississippi, since classes came back from summer break on August 9, around five per cent of all students have been asked to quarantine, according to data from the state’s health department. Less than 36 per cent of Mississippi residents are fully vaccinated.
State epidemiologist, Dr Paul Byers described the number of children now in quarantine as “dramatic”.
“That exceeds what we’ve experienced… when we were at our previous peak for the impact on the schools,” he told reporters on Wednesday.

A 13-year-old girl died over the weekend, Dr Byers said, adding that she was the fifth child to die because of the virus in the state.
Mississippi’s only paediatric hospital has had to turn parts of a garage into a field hospital due to the rise in admissions.
The southern US state is just the latest to face such outbreaks among children.
In one school district in Florida, over 10,000 children and staff are being told to stay home. The outbreak made the Hillsborough County School Board vote on Wednesday to require masks in schools.
Hillsborough County joins others in the Sunshine State, like Miami-Dade, in approving such a policy despite threats from Florida’s Republican governor to punish leaders who enact mask mandates in schools. (BBC)