The delta variant of the coronavirus is the “greatest threat” to eliminating Covid-19 in the United States, the nation’s leading infectious disease expert Dr. Anthony Fauci said Tuesday.

The variant, which was first detected in India, is more contagious and causes more severe disease than other circulating variants, he said during a White House Covid-19 response team briefing.

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Cases of delta have doubled in the past two weeks in the U.S. As of June 19, more than 20 percent of new Covid-19 cases were caused by the variant, up from around 10 percent the week ending June 5. The Centers for Disease Control and Prevention deemed delta a “variant of concern” last week.

June 22, 202101:46

In the United Kingdom, the delta variant overtook the alpha, or B.1.1.7, variant, over two months. Delta cases now make up “well over 95 percent” of new cases in the U.K., Fauci said. The U.S. “has followed the U.K.” in terms of variants.

In the U.K., children and young adults are driving the surge of delta cases. People ages 20 and younger are not yet eligible for vaccination in the country.

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Vaccinations are available for anyone ages 12 and up in the U.S., and more than 70 percent of adults 27 and up will have received at least one dose by July Fourth, Jeffrey Zients, the head of the White House Covid-19 response team, said during the briefing.

But rates are lower among young adults ages 18 to 26, he said, and the U.S. will likely fall short of President Joe Biden’s goal of partially vaccinating 70 percent of all adults by Independence Day.

“With the delta variant now spreading across the country, and infecting younger people worldwide, it’s more important than ever that they get vaccinated,” Zients said.

Indeed, the “good news,” Fauci said, is that “all vaccines are effective against the the delta variant.”

Data from the U.K. have found that two doses of the Pfizer-BioNTech vaccine are 96 percent effective against hospitalization from delta.

“We have the tools, so let’s use them and crush the outbreak,” Fauci said.

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