The Delta variant, which was first detected in India, now accounts for more than 6% of all infections in the United States, according to the Centers for Disease Control and Prevention. And this highly transmissible variant may be responsible for more than 18% of cases in some Western states.

The variant, also known as B.1.617.2, is spreading rapidly in the U.K., and has quickly become the dominant strain there, responsible for more than 60% of infections and causing surges in some parts of England.

"We cannot let that happen in the United States," says Dr. Anthony Fauci.

Speaking at a White House COVID briefing Tuesday, Fauci warned that the Delta variant may be associated with more severe disease and a higher risk of hospitalization.

The good news is the vaccines look like they can protect people against the Delta variant. A new study from Public Health England showed two doses of the Pfizer-BioNTech vaccine were 88% effective against symptomatic disease from the Delta variant compared to 93% effectiveness against the Alpha variant, the variant first detected in the U.K. Effectiveness declined to 33% after just one dose.

Fauci urged everyone who has received the first dose of the Pfizer or Moderna vaccines to make sure to sign up for a second. "And for those who have still not been vaccinated yet, please get vaccinated," he said.

He says vaccination is the best way to protect yourself and to stop this variant from spreading and becoming dominant in the U.S.

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