There is a risk that the highly transmissible delta variant first identified in India could become the dominant strain in the U.S. if vaccination rates lag, Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, said during a June 8 White House briefing.
The variant accounts for about 6 percent of COVID-19 cases genetically sequenced in the U.S., according to the CDC. The U.K. was in a similar situation a few weeks ago, but now the delta variant is rapidly emerging as the country's dominant strain. The variant now accounts for about 60 percent of cases in the U.K., with peak transmission occurring among 12- to 20-year-olds, according to Dr. Fauci.
"We cannot let that happen in the United States," Dr. Fauci said, emphasizing the importance of vaccinating younger Americans.
Two doses of Pfizer's vaccine is 88 percent effective against the variant two weeks after the second dose. Three weeks after the first Pfizer dose, the vaccine is only 33 percent effective against symptomatic cases from the delta variant.