Nearly 350 children are currently hospitalized with COVID-19 in Texas, state data shows.

According to the Texas Department of State Health Services' online COVID-19 dashboard, which was last updated on Sunday afternoon, there are 345 pediatric patients in hospitals across the Lone Star State. That number was up from 282 on Thursday afternoon.

The data also shows there are 73 staffed pediatric intensive care unit beds available in all of Texas.

Since the new school year began in Texas last month, some 52,000 students have tested positive for COVID-19, according to the data.

-ABC News' Gina Sunseri

Booster shots for the Moderna vaccine will have to wait at least one week after the president's Sept. 20 target because of the delay in submitting data, Dr. Anthony Fauci said Sunday.

Fauci told CNN that Pfizer was able to submit its data to the Food and Drug Administration about their mRNA vaccine booster shot earlier, and "it's been examined and ready to go." Moderna is behind in submitting its data causing the delay.

"What you might see is rather than the simultaneous rolling out of the booster program of both those products you may have be sequential by about a week or two," he said. "I don't think that is a major issue there, but we would have liked to have seen it happen all together simultaneously."

Three Florida school districts have filed a legal challenge against the state health department, seeking to invalidate an emergency rule that allows parents to opt out of mask mandates.

The petition, filed Friday, argues that the emergency rule -- issued after Gov. Ron DeSantis ordered the health department to protect parents' choice when it comes to masking their children -- exceeds its authority and is invalid.

The school districts in Alachua, Broward and Orange counties, which all require students and staff to wear masks, requested that an administrative judge hear the case.

Florida's education commissioner has withheld the salaries of school board members in Alachua and Broward counties over their mask mandates -- and has threatened similar action in Orange County.

Last week, a Tallahassee judge ruled in favor of a group of parents who sued the state over its ban on mask mandates. That ruling is being appealed.

-ABC News' Will McDuffie

Over 2.1 million people were screened at U.S. airport security check points Friday -- the highest checkpoint volume since Aug. 15, Transportation Security Administration spokesperson Lisa Farbstein said.

Americans have flocked to airports to travel for the Labor Day weekend despite the threat of the delta variant and surging COVID-19 cases and hospitalizations.

The U.S.’ daily case average remains around 153,000 cases a day, up by approximately 964% in the last two months.

Overnight Friday, the U.S. recorded its second single-highest day of COVID cases this week with more than 170,000 new cases reported.

Every state in the country is currently experiencing high community transmission. The South still leads the country with the highest case rates. Tennessee, and South Carolina currently have the country's highest case rate, followed by Mississippi, Florida, Georgia and Wyoming, all with case rates above 600 per 100,000 people.

-ABC News' Ahmad Hemingway and Arielle Mitropoulos

The COVID-19 vaccines' ability to keep people out of the hospital appears to be dropping slightly, particularly for those 75 and older, although the vaccines still remain highly effective at preventing serious illness, according to an analysis by the Centers for Disease Control and Prevention presented Monday during an advisory panel.

The CDC has previously estimated that 97% of people in the hospital being treated for COVID-19 are unvaccinated, but that data was collected before the spread of delta, a hyper-transmissible variant that many doctors have warned appears to be making people sicker.

Health experts are also concerned that a person’s immunity could be waning over time, particularly among older people whose bodies are less likely than young people to develop a strong immune response to the vaccines.

The latest CDC analysis estimates that the ability of the COVID vaccines to keep a person out of the hospital is now between 75% to 95%.

For people older than 75 in particular, vaccine effectiveness against hospitalization experienced the steepest decline, from more than 90% to 80% between June and July.

However, the vaccines still remain highly effective at preventing serious illness, according to the briefing. "COVID-19 vaccines continue to maintain high protection against severe disease, hospitalization, and death," the CDC notes.

-ABC News’ Anne Flaherty