COVID-19 updates: 345 children currently hospitalized with coronavirus in Texas

Florida Gov. Ron DeSantis filed an appeal against a court ruling invalidating his ban on student mask mandates Thursday evening.

The governor had banned school districts from implementing mask mandates without a parent opt-out. 

The move unleashed a stay of proceedings that enables the state to continue punishing districts, at least until Wednesday, when a judge will decide whether to vacate the stay. 

In the meantime, school board members across the state could continue to lose their salaries if their schools set mask mandates -- a punishment given to board members in two counties and threatened to those in eight others.

The appeal comes a week after Judge John C. Cooper found that a blanket ban on face masks in schools "does not meet constitutional muster.”

-ABC News' Will McDuffie

The country’s COVID death toll has risen to more than 643,000 and the number of cases stands at 39.5 million, according to data from Johns Hopkins University.

That means 1 out of 8 Americans has tested positive for COVID-19 and 1 out of 510 Americans has died of the virus. 

Heading into Labor Day weekend health experts are urging the public, especially the unvaccinated, to act responsibly as the delta variant continues to fuel infections. 

Holidays have proven to be a catalyst for virus spread in the U.S. 

Last summer, shortly after Labor Day, the U.S. fell into its most significant viral surge of the pandemic. 

Between the week following last Labor Day and Thanksgiving alone, the nation's daily case average surged by more than 400%.

-ABC News' Arielle Mitropoulos

Over "1.40M doses reported administered over yesterday's total, including 550K newly vaccinated and 96K additional doses," White House COVID-19 data director Cyrus Shahpar said Friday. 

That's the highest dose total since July 1, he said.

So far over 175 million people, or 61.9% of the eligible population, are fully vaccinated.

A new study by the U.S. Centers for Disease Control and Prevention estimates that roughly 83% of blood donors in the nation have either been vaccinated against COVID-19 or were previously infected with the virus.

This, however, does not mean that more than 80% of Americans are immune from infection. That's because neither vaccination nor prior infection provides 100% protection -- antibodies are just one part of the overall immune response, and immunity wanes over time. The analysis also may overestimate the portion of people with antibodies because blood donors may be more likely to be vaccinated or have previously been infected.

The study, posted online Tuesday by JAMA Network Open, a monthly open access medical journal published by the American Medical Association, took a snapshot of the presence of antibodies from COVID-19 vaccination or prior infection in about 1.4 million donated blood samples from across the United States. The repeated cross-sectional analysis was conducted each month during July 2020 through May 2021, before delta became the predominant variant of the novel coronavirus in the U.S.

The study shows that the number of blood donors who tested positive for antibodies, indicating either vaccination or prior infection, has gone up over time, from 3.5% in July 2020 to 20.2% for infection-induced antibodies and 83.3% for both infection- and vaccine-induced antibodies in May 2021.

Being vaccinated offers better protection compared to prior infection, and it's recommended that people who have previously contracted COVID-19 should still get inoculated.

-ABC News' Katie Bosland and Sony Salzman