Though it is just one of many variants to have arisen during the pandemic, the delta variant is considered one of the most alarming. (Video: The Washington Post)

A highly transmissible coronavirus variant first identified in India accounts for 6 percent of new infections in the United States, the Biden administration said Tuesday. Yet vaccines appear to be highly effective against this version of the virus that has quickly spread into Great Britain and elsewhere.

Anthony S. Fauci, the nation’s leading infectious-disease expert, revealed the extent of the variant’s push into the United States, but said it appears to be slowed by vaccines.

“It’s essentially taking over” in the United Kingdom, Fauci said at a briefing for reporters. “We cannot let that happen in the United States, which is such a powerful argument” for vaccination, he said.

Fauci referred to data from Britain’s public health agency that shows two doses of the vaccines made by Pfizer-BioNTech and AstraZeneca are 88 percent effective in preventing symptomatic disease caused by the new variant, also known as delta. He said in an interview that the Pfizer data would be similar for Moderna’s product, which also is an mRNA vaccine.

What we know about the highly infectious coronavirus delta variant

But one vaccine dose offers just 33 percent protection, the data shows, a reminder of how strongly the second shot boosts immunity to the virus, Fauci said. With the United States in the midst of providing vaccines to adolescents and other people who have waited to get them, second doses are critical, he said.

Fauci, head of the National Institute of Allergy and Infectious Diseases, said virus transmission in Britain is “peaking” among 12- to 20-year olds, one of the groups that the United States is rushing to vaccinate. In Britain, he said, the delta variant now accounts for more than 60 percent of new infections. Some British scientists are warning that the country faces a third wave of infection.

The numbers are based on genomic surveillance of cases in both countries.

At the same briefing, Rochelle Walensky, director of the Centers for Disease Control and Prevention, reported the continuing decline of coronavirus cases in the United States. She said “just over 10,000 new cases of covid-19,” the disease caused by the virus, were reported Monday, and the rolling seven-day average of cases totaled 13,277.

The latter number, considered more reliable, marked the first time the average has fallen below 15,000 since March 27, 2020, Walensky said. Daily hospitalizations have declined 83 percent from their peak on Jan. 9, she said, and the seven-day average of deaths from the disease is 379 per day.

“Each week there are more and more data to demonstrate the impact vaccination has on preventing disease and moving us out of this pandemic,” Walensky said.

But with the daily vaccination average falling below 1 million recently, the administration continues to expand efforts to bring the vaccine to hard-to-reach groups, including people who need transportation to vaccine sites and workers who must take time off to be vaccinated. Biden has set a goal of vaccinating 70 percent of U.S. adults by July 4 a goal that is in jeopardy. So far 13 states have reached that milestone.

Vaccination rates fall off, imperiling Biden’s July Fourth goal

Andy Slavitt, senior adviser to the task force, said the American Hospital Association will help employers find medical partners to open pop-up vaccine sites at workplaces during business hours, and Uber and Lyft will continue providing free transportation to vaccine centers through July 4.

Marcella Nunez-Smith, head of the coronavirus Health Equity Task Force, said pharmacies will be staying open late on Friday nights in June. More than half of doses administered at pharmacies in the past two weeks went to people of color, who trail Whites in receiving the vaccines, she said.

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