Dr. Rochelle Walensky, the head of the Centers for Disease Control and Prevention, told reporters on Thursday that the COVID-19 Delta variant is one of the most infectious respiratory viruses that she has seen in her 20-year career.

CLICK FOR THE LATEST ON THE CORONAVIRUS

She called the variant more "aggressive" and transmissible than earlier strains of the virus. The Biden administration has used the threat of the variant to underscore the importance of Americans getting vaccinated. 

PORTLAND SHOOTING LEAVES 1 WOMAN DEAD, 6 HURT: POLICE; MAYOR TALKS ‘GUN VIOLENCE PROBLEM’ IN NEWS CONFERENCE 

Kristen Choi, an assistant professor at UCLA School of Nursing, told Yahoo Finance Live that about 99% of those hospitalized are unvaccinated.  The report pointed out that the vaccination effort in the U.S. has slowed and about 57.1% of the population over 12 is vaccinated.

Forty percent of this week’s coronavirus cases came from FloridaTexas and Missouri, White House COVID-19 Response Coordinator Jeff Zients said. 

The Washington Post zeroed in on D.C. and reported that 375,000 of the city’s 692,000 residents have been vaccinated. Of those, 200 have tested positive for the virus, 13 have been hospitalized and four have died.

CLICK HERE TO GET THE FOX NEWS APP

The paper said despite the number of breakthrough cases, health officials say the numbers show that the vaccines have been effective.

"No vaccine is 100% percent effective, and we know this coming in," Ankoor Shah, the head of D.C.’s vaccine program, told the paper.

The Associated Press contributed to this report