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

This year’s Made In America festival over Labor Day weekend in Philadelphia will go on with COVID-19 restrictions.

Despite surging delta variant cases and flooding from the Schuylkill River that inundated the Ben Franklin Parkway with water, the festival will continue, officials said. 

"I think it's good for the city to have this kind of event, so we can celebrate a little bit even in the midst of potential tragedy. Jay-Z, Beyonce, the Biebs (Justin Bieber) is coming," Philadelphia Mayor Jim Kenney said Friday. “It'll be fun for a change...be nice to have some fun, wouldn't it?"

Roc Nation, which is producing the two-day festival, said all attendees will need to wear masks. Attendees will also have to show proof of a negative COVID-19 test or printed proof of full COVID-19 vaccination to get in. 

"The negative COVID-19 test result must be obtained within 48 hours of attending the Made In America festival," said Roc Nation on the festival’s website. 

Philadelphia officials also updated the city’s mask mandate in August to require masks at all non-seated outdoor events with over 1,000 attendees.