CNN  — 

Millions of school-age children in the United States are still unvaccinated against Covid-19 as many prepare for a return to school.

A new CNN analysis finds that less than half of children and teens are fully vaccinated against Covid-19, and only a tenth have been boosted.

Many of the nation’s largest school systems – including Los Angeles Unified, City of Chicago, Miami-Dade County and Clark County in Nevada – start school next month.

Covid-19 cases are rising across the United States once again, driven by the Omicron subvariant BA.5, the most transmissible strain of the coronavirus yet. More than 14 million children have tested positive for Covid-19 since the onset of the pandemic, according to available state reports; more than 311,000 of these cases have been added in the past four weeks, the American Academy of Pediatrics reported as of Thursday.

Federal health officials urge those who are eligible to stay up to date on Covid-19 vaccinations by getting boosted.

The US Centers for Disease Control and Prevention considers someone “fully vaccinated” if it has been at least two weeks since they had a second dose of the Moderna or Pfizer/BioNTech coronavirus vaccine. They are “up to date” on their vaccinations if they’ve had the booster doses that they’re eligible for.

Everyone 6 months and older is eligible for Covid-19 vaccination, and those 5 and older are eligible for a booster.

About 23.9 million 5- to 17-year-olds are fully vaccinated against Covid-19, according to data posted Thursday by the CDC. That represents about 45% of that age group. About 22 million of them are eligibl