Masks will be required in all Pennsylvania schools and child care programs effective Sept. 7, Gov. Tom Wolf announced Tuesday.

"My office has received an outpouring of messages from parents asking us to protect children by requiring masks in schools," Wolf tweeted. "I preferred for local school boards to make this decision. But an aggressive nationwide campaign is pressuring school districts to adopt unsafe policies."

Mississippi has the country's highest COVID-19 case rate, followed by Florida, Kentucky and Louisiana, according to federal data.

With more than 101,000 Americans now hospitalized with COVID-19, the U.S. is steadily approaching its hospitalization peak from early January, when more than 125,000 patients were hospitalized at one time, according to federal data.

A little over two months ago, less than 12,000 patients were in U.S. hospitals, according to federal data.

But there has been improvement when it comes to vaccinations.

One week after the FDA fully approved the Pfizer vaccine, initial data from an ABC News analysis indicates that the U.S. has seen a slight uptick in the average number of Americans going out to get their first vaccine dose.

In the week prior to the full approval, an average of about 404,000 Americans were initiating vaccination each day. Now, about 473,000 Americans are getting their first shot each day -- a 17% increase.

-ABC News' Arielle Mitropoulos

Fifteen people were charged Tuesday in what the Manhattan District Attorney’s Office called a fake vaccine card conspiracy.

Among those charged is a woman who allegedly sold 250 fake cards on Instagram, believed to be among the first alleged seller of phony vaccine cards charged in
the country.

Manhattan District Attorney Cy Vance said in a statement, "We need companies like Facebook to take action to prevent the fraud happening on their platforms."

"Making, selling, and purchasing forged vaccination cards are serious crimes with serious public safety consequences. This investigation is ongoing," Vance continued. "If you are aware of anyone selling fake vaccination cards, please call my Office’s Financial Frauds Bureau at .”

-ABC News' Aaron Katersky

New York Gov. Kathy Hochul said Tuesday that unvaccinated public and charter school employees must undergo weekly testing.

"I think that's a compromise,” she said.

Hochul is also working to establish vaccine requirements for all staff at state-regulated facilities and congregate settings. New York officials announced last week that all health care facility staff must be vaccinated.

-ABC News' Aaron Katersky

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