Delta COVID-19 Variant Is 'Greatest Threat In US'; Pfizer 88% Effective Against Strain: Fauci

White House Chief Medical Adviser Dr. Anthony Fauci on Tuesday warned against the threat that the COVID-19 Delta variant poses to the United States.

The B.1.617.2 variant, now known as the Delta variant, was first detected in India. It is currently believed to be the most transmissible variant and currently accounts for 20% of all new cases in the United States.

At a White House news conference on Tuesday, Fauci said the more contagious variant appears to be following a pattern similar to the Alpha variant which caused a COVID-19 outbreak in the U.K.

“Similar to the situation in the U.K., the Delta variant is currently the greatest threat in the U.S. to our attempt to eliminate Covid-19,” Fauci said.

Scientists in the U.K. say the Delta variant is 60% more contagious than the Alpha variant. The Alpha variant, first detected in the United Kingdom, is believed to be 43% to 90% more transmissible than the original COVID-19 strain, noted WebMD.

During the news conference, Fauci also urged Americans to use “the tools” the country has to crush the variant. He also noted that the Pfizer/BioNTech COVID-19 vaccine is highly effective in protecting recipients against COVID-19.

“The effectiveness of the vaccines, in this case, two weeks after the second dose of Pfizer-BioNTech was 88% effective against the delta and 93% effective against alpha when dealing with symptomatic disease,” the nation’s top infectious disease expert said.

Other health experts echoed Fauci’s warning, with Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention, saying that she anticipates the Delta variant to be the predominant cause of infections in the country.

"It's more transmissible than the alpha variant, or the U.K. variant, that we have here. We saw that quickly become the dominant strain in a period of one or two months, and I anticipate that is going to be what happens with the Delta strain here,” Walensky said in an interview on “Good Morning America.”

William Lee, vice president of science at Helix, said he believes the Delta variant could be a few weeks away from becoming the dominant strain in the U.S.

"It's so transmissible that, unless your vaccination rates are high enough, you will still have outbreaks,” Lee told CNN.