Nearly 600 patients wait for hospital beds in Houston following surge in COVID cases

The proportion of hospitalized COVID-19 cases among vaccinated people has risen sharply since spring, coinciding with the sudden rise of the delta variant, according to the CDC's internal briefing slides reviewed by ABC News. 

The finding doesn’t mean the vaccines aren’t working. People are still considerably less likely to wind up in the hospital or die if they are vaccinated, health officials have said.

The reality of more breakthrough cases also could be tied to the larger number of Americans getting vaccinated. While breakthrough cases remain relatively uncommon, the more people in the U.S. who are vaccinated increases the chances for breakthrough cases to be counted. 

According to the CDC, vaccinated individuals who end up hospitalized tend to be elderly, medically vulnerable or live in long-term care facilities. They also are more likely to be asymptomatic and are hospitalized for reasons other than COVID-19.

On July 17, CDC Director Rochelle Walensky estimated that 97% of hospitalizations were occurring among people who weren’t immunized.

-ABC News' Anne Flaherty, Cheyenne Haslett, Eric Strauss

Dr. Anthony Fauci supports a mask mandate for teachers, he told MSNBC's "Morning Joe" Tuesday.

"We are in a critical situation here. We've had 600,000+ deaths and we are in a major surge now as we're going into the fall," Fauci said. "I know people must like to have their individual freedom and not be told to do something, but I think we're in such a serious situation now that, under certain circumstances, mandates should be done."

Fauci said it's only a matter of time until the FDA approves the vaccine and people shouldn't use that as a reason to delay getting the shot.

"There's no doubt that these vaccines are going to get fully approved," he said. "You should consider this as good as fully approved and get vaccinated."

-ABC News' Cheyenne Haslett

Only two intensive care unit beds were available for COVID-19 patients in hospitals in the Austin area Monday night, Austin-Travis County Health Authority Dr. Desmar Walkes said, according to ABC Austin affiliate KVUE.

There were 551 COVID-19 patients in area hospitals Monday, including 91 in the ICU, KVUE reported.

In the North Texas region, there are only two pediatric ICU beds available, Dallas County Judge Clay Jenkins said, according to ABC Dallas affiliate WFAA.

Florida currently has the nation's highest COVID-19 case rate, followed by Louisiana, Arkansas, Alabama, Missouri, Mississippi and Texas, according to federal data.

Across the country, 90% of counties -- home to 98% of the U.S. population -- have reported high (a seven-day new case rate ≥100) or substantial (a seven-day new case rate between 50-99.99) community transmission in the last week.

According to federal data, these states have high or substantial transmission in every county: Arizona, Arkansas, Connecticut, Delaware, Florida, Georgia, Indiana, Louisiana, Mississippi, New Jersey, Rhode Island, South Carolina, Tennessee, Utah, Washington and Wyoming.

-ABC News' Arielle Mitropoulos