The delta variant, a highly contagious strain of COVID-19 first detected in India, now makes up approximately 83% of coronavirus cases nationwide, according to the U.S. Centers for Disease Control and Prevention. 

What You Need To Know

  • CDC Director Dr. Rochelle Walensky on Tuesday said the highly contagious delta variant now makes up 83% of sequenced COVID-19 cases nationwide

  • Walensky said the number is a “dramatic increase” from the week of July 3, when the delta variant made up nearly 50% of sequenced cases nationwide

  • In some parts of the country, where vaccination rates have lagged, the incidence rate of the delta variant is even higher

  • Dr. Anthony Fauci and Sen. Rand Paul got into a heated exchange at the hearing over gain-of-function research, with the Kentucky Republican accusing the White House's chief medical advisor of lying to Congress

In testimony before the Senate Health Committee, CDC Director Dr. Rochelle Walensky said the number is a “dramatic increase” from the week of July 3, when the delta variant made up nearly 50% of sequenced cases nationwide.

In parts of the country where vaccination rates have lagged, the percentage is even higher, Walensky noted. 

“The message from CDC remains clear: The best way to prevent the spread of COVID-19 variants is to prevent the spread of disease, and vaccination is the most powerful tool we have,” she told Senators on Tuesday. “We must continue to expand vaccine coverage by building trust and confidence in COVID-19 vaccines.” 

Walensky added that the “overwhelming majority” of COVID-19 deaths are occuring in the unvaccinated population.  

Dr. Anthony Fauci, the nation’s leading infectious disease expert, also testified in front of the committee on Tuesday, saying of the delta variant: “The reason it's so formidable is the fact that it has the capability of transmitting efficiently from human to human in an extraordinary manner well beyond any of the other variants that we've experienced up to now.”

To date, the delta variant has been detected in at least 90 countries across the world.

The hearing, at times, got very contentious, particularly between Dr. Fauci and Kentucky Sen. Rand Paul, who have traded barbs before at numerous Congressional hearings.

On Tuesday, the two argued over whether or not the National Institutes of Health funded controversial gain-of-function research — the practice of enhancing a virus in a lab to study its potential impact in the real world — at a Wuhan virology lab. U.S. intelligence agencies are currently exploring theories that an accidental leak from that lab could have led to the global pandemic.

The Kentucky Republican accusing the White House's chief medical advisor of lying to Congress.

"Dr. Fauci, as you're aware, it is a crime to lie to Congress," Sen. Paul said. "On May 11, you stated that the NIH has not ever, and does not now fund game to function research and the Wuhan Institute of Virology. And yet, gain of function research was done entirely in the Wuhan Institute."

Dr. Fauci said in May that the NIH "has not ever and does not now fund gain of function research in the Wuhan Institute of Virology." Paul asked Dr. Fauci if he would like to retract his earlier testimony.

The nation's leading infectious disease expert vehemently denied any wrongdoing: "I have not lied before Congress. I have never lied. Certainly not before Congress. Case closed."

"Sen. Paul, you do not know what you are talking about, quite frankly, and I would like to say that officially," Dr. Fauci said, asserting that the study to which Sen. Paul was referring did not constitute gain-of-function research. "You do not know what you are talking about."

The exhange got uglier, with Sen. Paul accusing Dr. Fauci of "trying to obscure responsibility for 4 million people dying around the world from a pandemic."

"You are implying that what we did was responsible for the deaths of individuals," Dr. Fauci replied. "I totally resent that, and If anyone is lying here senator, it is you."

"This is a pattern that Senator Paul has been doing now at multiple hearings based on no reality," Dr. Fauci said of the Kentucky lawmaker's rhetoric.