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

A Centers for Disease Control and Prevention advisory panel is expected to meet later this week to discuss the possibility of COVID-19 vaccine booster shots for people who are severely immunocompromised.

The meeting of the CDC’s ACIP panel -- scheduled for Friday from 11 a.m. to 2 p.m. -- will be closely watched as the nation awaits a decision by federal regulators on whether to authorize a booster shot for certain vulnerable groups.

If the Food and Drug Administration greenlights boosters, the ACIP panel would have to make its own recommendation on who should get the shot and what factors they might want to consider. Those recommendations are typically adopted by the CDC as nationwide public health guidance.

During a meeting last month, ACIP members agreed an extra shot probably does help protect immunocompromised people but that more research was needed*.*

-ABC News' Anne Flaherty

The Centers for Disease Control and Prevention estimates that more than 1 million people who have received the Moderna or Pfizer vaccine have gone back for an unauthorized third booster shot. 

Florida is among the states reporting the highest number of people opting for a booster shot, followed by Ohio, California, Illinois and Tennessee.

The estimated 1.1 million, included in an internal CDC briefing document reviewed by ABC News, likely is an undercount because although it counts Moderna and Pfizer shot recipients it ignores people who may have received the one-shot Johnson & Johnson vaccine and got another shot.

It’s also unclear whether people who received a third shot did so under the direction of a doctor. The Food and Drug Administration hasn’t authorized a third shot to boost immunity, although there are reports of some physicians encouraging severely immunocompromised patients to do so.

Boosters for the immunocompromised may be recommended by the FDA within weeks.

-ABC News' Anne Flaherty, Eric Strauss

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