Without control over the community spread of the delta variant, the virus has "ample opportunity to mutate," so "you may sooner or later get another variant," Dr. Anthony Fauci told "Good Morning America."

Fauci warned that it's possible a new "variant might be in some respects worse than the already very difficult variant we're dealing with now, which is a major reason why you want to completely suppress the circulation of the virus in the community."

There are still about 93 million eligible Americans who have not gotten vaccinated.

Fauci added, "People who say, 'I don't want to get vaccinated because it's me and I'll worry about me, I'm not having any impact on anybody else,' that's just not the case."

-ABC News’ Cheyenne Haslett

There are 5,042 new positive COVID-19 cases in Tokyo as of Thursday, according to the city's coronavirus information website.

Of those cases, 135 are severe and one has resulted in death.

It's a new record for Tokyo and a 178% increase since last Thursday, as the highly contagious delta variant spreads rapidly across the globe.

Texas reported 15,558 new COVID-19 cases Wednesday, the highest one-day count since Feb. 3, according to state health records.

The state has seen a major jump in cases in the last month, brought on by the delta variant, according to officials.

The seven-day average of new daily cases has increased from about 1,500 on July 2 to nearly 10,000 on Aug. 3, according to state health data.

As of Wednesday, 62.58% of Texas residents 12 and older have received at least one shot, according to the state health department.

Hundreds of student and staff members from the Marion School District in Arkansas are now quarantined in only the second week of the school year, officials announced.

The state has a ban on school districts imposing a mask mandate.

On Tuesday, the district said 253 students would begin their two-week quarantine due to 15 cases that were reported in the schools. This came after 168 students were already quarantined last week.

"If all students and teachers had been wearing a mask appropriately- then today's 15 positive cases would be isolated- but there would be no resulting quarantines for anyone else," the district said in a statement.

Arkansas Gov. Asa Hutchinson told reporters Tuesday he regretted signing the bill that banned masks in schools and urged the state legislature to amend the law to give schools the option.

In Louisiana, which has the nation's highest case rate per 100,000 residents, COVID-19 hospitalizations are reaching peak levels, with more than 1,700 patients now receiving care.

"We're seeing people that are way too young to be so sick," David Wrightson, a respiratory therapist and ECMO (extracorporeal membrane oxygenation) specialist for the Willis-Knighton Health System in Shreveport, Louisiana, told ABC News. "We see families destroyed. We see children without one or more parent because of this virus. We see a new mom who will never go home to see her newborn, will never see her child grow up."

He went on, "When you see someone that's 30 years old with no medical problems at all, nobody knew anything was wrong, and we have this person literally on death's doorstep, doing everything in our power to turn them around and return them to their family. The vaccine is something worth getting."

More people need to see and understand the reality of this disease, he said.

"I wish I could show them a few steps in our day to see what we see and to see what we have to do, and to go home at night and, and have nightmares about those things, and sometimes cry yourself to sleep," he said.

-ABC News’ Erica Baumgart and Arielle Mitropoulos